Tabs configuration, extracted from About:config entries


This page was created to be a companion of my page on Tabbed Browsing in Firefox.

The table on this page consisting of selected tab and window items has been extracted from
which is part of the MozillaZine_Knowledge_Base article

Heuer's Razor:  "If it can't be turned off, it's _not_ a feature." (is often quoted in Developer groups.)

This listing is basically comprised of entries selected from the mozillaZine article About:config entries dealing with tabs and is mainly from the following groups:

To view table and your own settings at the same time, you might want to install the Split Browser extension and split the screen vertically with the table as the main at the bottom so it is with Find, and with the split about:config at the top, and descriptions such as on this page below.  (for more information see firefox.htm page)

Note:  Spaces between the dots in preference names exist purely for word-wrapping.  They are actually not present and should not be thought as so.

To find values related to an about:config configuration entries

Use your browser's FIND to find variables or descriptions matching a one word or character string.  For instance you might want to use FIND openintab in browser, and filter:  openintab in the about:config list where "" has extra spaces as "browser. search. openintab".

To change a configuration setting double-click on the variable and change the value (right-click context menu also works).  If the type is Boolean a double-click will toggle the value immediately, so always keep an eye on the value or the "user set" / "default" indication for each variable.

number rows   Click once on the bookmarklet at the left to Number the rows of each tableDetails of Text and Data Bookmarklets at also see my Keyword shortcuts page to invoke bookmarklets on any page.

Name Type Meaning of Values
browser. backspace_action Integer Determines the behavior of the backspace key
0: Goes back in history
1: Acts as Page Up
2 (and above): Does nothing
Note: See bug 301248 (Mozilla Suite)
browser. block. target_new_window Boolean True:  Links with target set to _blank will open in the current tab instead of a new window.
False:  Links with target set to _blank will open in a new window.
Note:  No longer in use. Use instead.
browser. display. focus_background_color String The default color for the background of focused elements as a hex code. Default value is #117722. Requires that browser.display.use_focus_colors be true
browser. display. focus_ring_on_anything Boolean True:  Display the focus ring (normally only shown on links) on anything
False (default):  Display the focus ring on links only
browser. display. focus_ring_width Integer Determines the display of the focus ring around focused elements.
0:  Hide focus ring
1 (default):  Dots around focused elements will be displayed with a 1 pixel border
(n):  Display dots with a width of n pixels around focused elements
browser. display. focus_text_color String The default color for the text of focused elements as a hex code. Default value is #ffffff. Requires that browser.display.use_focus_colors be true
browser. display. use_focus_colors Boolean True:  Set colors on focused items according to preferences
False (default):  Do not set colors on focused items
browser. fullscreen. animateUp Integer Controls toolbar and tab strip animation while in Full Screen.
0: No toolbar and tab strip animation
1 (default): Animates only first collapse.
2: Animates each collapse.
browser. fullscreen. autohide Boolean Hides toolbar and tab strip when entering Full Screen.
True (default): Shows toolbar and tab strip.
False: Hides toolbar and tab strip
browser. link. open_external Integer Where to open links sent to the browser from an external application
2:  Opens external links in a new window
3:  Opens external links in a new tab
1 (or anything else) (default):  Opens external links in current window
Note:  In Firefox 1.5, this can be changed via "Tools → Options → Advanced → Tabbed Browsing → Open links from other applications in:"
This option is mentioned under Browser Behavior in Firefox Help:  Tips & Tricks
Possibly removed in Firefox 3.1 see bug: 324164
Bug 468973 - 3.1b2 doesn't honor = 2 (Open in New Window)
browser. link. open_newwindow Integer Where to open links that would normally open in a new window
2:  In a new window
3 (default):  In a new tab
1 (or anything else):  In the current window
browser. link. open_newwindow. restriction Integer Firefox and SeaMonkey only. Source:  The Burning Edge.
0 (Default in Firefox 1.0.x and SeaMonkey):  Force all new windows opened by JavaScript into tabs.
1:  Let all windows opened by JavaScript open in new windows. (Default behavior in IE.)
2 (Default in Firefox 1.5):  Catch new windows opened by JavaScript that do not have specific values set (how large the window should be, whether it should have a status bar, etc.) This is useful because some popups are legitimate — it really is useful to be able to see both the popup and the original window at the same time. However, most advertising popups also open in new windows with values set, so beware.
This option is mentioned under Browser Behavior in Firefox Help: Tips & Tricks
browser. link. open_newwindow. ui Integer Determine which new window open options are available from the UI. No longer used in Firefox 1.0. Default value is 3.
browser. search. openintab Boolean True:  When performing a search from the Search Bar, open the results in a new tab.
False (default):  Open search results in the current tab/window.
Note:  Firefox nightly trunk builds only.
If you foolishly installed Tab Mix Plus then controlled by
browser. search. order. (digit) String (digit) is used to weight the search engine specified by the value for sorting in the list of search engines.
browser. sessionhistory. cache_subframes Boolean True:  Cache the content viewer (when browser.sessionhistory.max_total_viewers is greater than 0) for subframes
False (default):  Opposite of the above
Note:  Firefox 1.5 and above only.
browser. sessionhistory. max_entries Integer The maximum number of pages in the browser's session history, i.e. the maximum number of URLs you can traverse purely through the Back/Forward buttons. Default value is 50.
browser. sessionhistory. max_total_viewers Integer Determines the maximum number of content viewers to cache for "bfcache" (fast back/forward navigation). Default value is -1 (calculate based on available memory). All values less than 0 are equivalent.
Note:  Firefox 1.5 and above only.
Browser. sessionstore. enabledBooleanTrue (default):  Record information about the current browser session (open windows and tabs, history, cookies, form data) so it can be restored if necessary.
False:  Disable the Session Restore service completely.
* For the browser session to be restored at startup after a crash, browser.sessionstore.resume_from_crash must be true.
* For the browser session to be restored at startup normally, must be 3.
Browser. sessionstore. resume_from_crashBoolean Firefox 2.0 introduces a built-in Session Restore feature, allowing the user to continue browsing from where they left off if browser restarts.
True (default):  Restore the previous session when the browser starts after a crash.
False:  Do not restore the previous session.
* browser.sessionstore.enabled must be true for this preference to have an effect.
* Related preferences:  | browser.sessionstore.enabled | browser.sessionstore.interval | browser.sessionstore.max_tabs_undo | browser.sessionstore.max_windows_undo | browser.sessionstore.resume_session | browser.sessionstore.resume_session_once |
browser. startup. homepage String URL of homepage, or pipe (|)-separated list of URLs to open in tabs when going to the homepage
In SeaMonkey (or at least in SeaMonkey 2 and above), this is the URL of your first or only homepage tab. If you have a multitab homepage, additional URLs are in browser.startup.homepage.1, browser.startup.homepage.2, etc.
Note: This can be changed in Firefox via "Tools → Options → Main (Firefox 1.5 and 1.0.x: General) → Homepage" and in SeaMonkey via "Edit → Preferences → Browser → Home Page".
Browser.startup.pageIntegerEach time the web browser starts, this preference is consulted to determine what to display. It has superseded browser.sessionstore.resume_session as the preference determining whether saved sessions are restored.
0:  Start with a blank page (about:blank).
1:  (default) Start with the web page(s) defined as the home page(s).
2:  Load the last visited page.
3:  Resume the previous browser session (Firefox only, implemented after Firefox 2 beta 1)
browser. tabs. autoHide Boolean Behavior for the tab bar when only one tab exists
True (default):  Hide the tab bar
False:  Always show the tab bar
Note:  In Firefox, this can be changed via "Tools → Options → Tabs → Always show the tab bar
(Firefox 2 and above) or Tools → Options → Tabs → Hide the tab bar when only one web site is open (Firefox 1.5).
browser. tabs.closeButtons Integer (Firefox 2.0) This preference controls how close buttons can be displayed on tabs.
0: Display a close button on the active tab only
1: (default) Display a close button on each tab
2: Don't display any close buttons
3: Display a single close button at the end of the tab bar (Firefox 1.x behavior)
browser. tabs. closeWindowWithLastTab Boolean (Firefox 3.5 and above) This preference controls whether closing the last tab, closes the window.
True: Close window when closing last tab (default)
False: Do not close the window when closing last tab (pre Firefox 3.5 behavior)
Note: Changing to False prevents Firefox from closing the window when you close the last tab such as with Ctrl+W, and subsequently from closing Firefox itself when closing the last tab of the last Firefox window.
browser. tabs. forceHide Boolean Display of the tab bar
True:  Hide the tab bar
False:  Show tab bar normally
Note:  This is not used to enable/disable the tab bar. It's used internally to decide whether or not to show the tabbed bar.
browser. tabs. loadBookmarksInBackground Boolean Focus behavior of new tabs from bookmarks & history
True:  When you open a bookmark in a new tab then that tab will load in the background without taking focus from the current tab.
False (default):  When you open a bookmark in a new tab then that tab will become the current tab.
Note:  you likely want to set this to same setting value as used in browser.tabs.loadInBackground (Bug 469456)
Note:  Firefox 1.0.x had a Tabs option for "Select New Tabs from Bookmarks or History"
browser. tabs. loadDivertedInBackground Boolean Determines behavior of pages normally meant to open in a new window (target="_new" or from an external program), but that have instead been loaded in a new tab.
True:  Load the new tab in the background, leaving focus on the current tab
False (default):  Load the new tab in the foreground, taking the focus from the current tab.
Note:  Setting this preference to True will still bring the browser to the front when opening links from outside the browser.
Note: target="_new" creates/reuses a window named "_new" and is frequently used by Google.   target="_blank" loads the designated document in a new, unnamed window [ [1]].
browser. tabs. loadFolderAndReplace Boolean True (default):  When opening a folder of bookmarks in tabs, the existing tabs will be replaced by the new bookmark pages.
False:  Existing tabs will be preserved when loading a folder of bookmarks. The bookmark pages will be loaded in tabs that are appended to the current tabs.
Even with the setting at True, if you don't want to lose the current tab, and want new tabs at end instead of adjacent to active tab use Ctrl+Shift+click on "Open all in Tabs" (or Ctrl+click ..., whichever shortcut will load new tab(s) in foreground is the only one that will work)
Bug 175124 - improve open in tabs behaviour,
browser. tabs. loadGroup Integer 0:  Append group to current tab set
1 (default):  Replace current tab set with group
Note: Mozilla Suite/SeaMonkey only.
browser. tabs. loadInBackground Boolean Focus behavior for new tabs from links
True (default):  Do not focus new tabs opened from links (load in background)
False:  Opposite of above
Note:  bookmarks & history can be opened similarly with browser.tabs.loadBookmarksInBackground
Note:  In Firefox, this can be changed via "Tools → Options → Tabs → When I open a link in a new tab, switch to it immediately (Firefox 2 and above)
browser. tabs. loadOnNewTab Integer Determines what will be displayed in a new tab
-1:  Browser startup page
0 (default):  Blank page
1:  Homepage
2:  Last visited page
Note:  Does not work in Firefox (see bug 269664).
Solutions: New Tab Homepage (7KB), or NewTabURL (47KB).
browser. tabs. opentabfor. bookmarks Boolean Controls if a clicked bookmark will open in a new tab when middleclicked.
Note:  Pref removed (obsolete). Functionality proposed as enhancement request.
browser. tabs. opentabfor. middleclick Boolean Determines the behavior of a link when middle-clicked.
True (default):  Opens link in new tab
False:  Opens link in new window
MenuEditor extension and Tab related extensions might remove control of Middle-click, since I don't use Firefox's middle-click -- can't tell whether true or not.
browser. tabs. opentabfor. searchdialog Boolean Determines whether to create a new tab for the search results from queries entered in the search dialog (used when the Search Bar is hidden)
Note:  Firefox 1.5 and above only.
browser. tabs. opentabfor. urlbar Boolean Pref removed (unused). Previously:
Determines the behavior of pressing Enter in the address bar or clicking the Go button.
True (default):  Open URL in new tab
False:  Open URL in current tab
Note:  Functionality proposed as enhancement request.
browser. tabs. selectOwnerOnClose Boolean In conjunction with several other improvements to tabbed browsing in Firefox 2.0, the behavior of closing tabs was changed. Previously, closing any tab would shift focus to the tab immediately to the right if possible; failing that, the tab to the left. Now, if a page that would normally have opened in a new window is opened in a tab and that tab is closed, focus is shifted to the tab that opened the window. This preference controls whether the old or new behavior is observed.

True - If new windows are diverted into new tabs and a resulting tab is closed, shift focus back to the tab that opened it. (Default)
False - When any tab is closed, shift focus to the adjacent right tab if it exists; otherwise, to the adjacent left tab.

browser. tabs. showSingleWindowModePrefs Boolean Determines whether to display "Single Window Mode" settings in preferences (see bug 266759).
True:  Show "Force links that open in new windows to open in..." options under "Tools → Options → Advanced → Tabbed Browsing"
False (default):  Opposite of above
browser. tabs. warnOnClose Boolean True (default):  The browser will prompt for confirmation when closing the browser when more than one tab is open.
False:  No warnings will be given when closing the browser with more than one tab.
Note:  In Firefox, this can be changed via "Tools → Options → Tabs → Warn (me) when closing multiple tabs" (Firefox 1.5 and above) or "Tools → Options → Advanced → Tabbed Browsing → Warn when closing multiple tabs" (Firefox 1.0.x)
browser. tabs. warnOnCloseOther Boolean True (default):  The browser will prompt for confirmation when closing all other tabs from the tab context menu ("Close Other Tabs")
False:  Opposite of the above
Browser.warnOnQuitBooleanWhen quitting Firefox via “File → Exit”, every open browser window will be closed. This preference determines (along with browser.tabs.warnOnClose) whether or not a warning dialog appears before this happens.
Possible values and their effects
True (default): Display a dialog before quitting, warning that all windows will be closed.
False:  Do not require confirmation from the user when quitting.
Caveats - If browser.tabs.warnOnClose is false, then this preference has no effect.
Browser. warnOnRestart BooleanTrue (default) Display a dialog before restarting the browser, warning that all windows will be closed.
False Do not require confirmation from the user when restarting.
UI — A checkbox labeled “Do not ask next time” appears on the confirmation dialog; when checked, this preference is toggled to false.
browser. windows. loadOnNewWindow Integer Set what should be displayed in a newly created window
-1:  Browser Startup Page
0:  Blank Page
1 (default):  Your Homepage
2:  Last Visited
browser. zoom. full Boolean True (Default): Full page zoom
False: Text zoom
browser. zoom. siteSpecific Boolean True (Default): Remember the zoom level on a per-site basis.
False: The zoom level should be applied on the current tab only.
dom. disable_window_open_feature. * Boolean Web page authors can disable many features of a popup window that they open. Setting these preferences to true will override the author's settings and ensure that that feature is enabled and present in any popup window. [1] [2] [3]
close:  Prevents the close button from being disabled.
directories:  Prevents the bookmarks toolbar from being hidden.
location:  Prevents the address bar from being hidden
Ignore "location=no" in the window features argument of and prevent popups from hiding the Location Bar (Default in Fx3).  False allows popups to hide the Location bar. (Default in Fx2) In Fx2 default was False, in Fx3 default is True.
menubar:  Prevents the menubar from being hidden.
minimizable:  Prevents popup window minimization from being disabled.
personalbar:  Prevents the bookmarks toolbar from being hidden.
resizable:  Prevents popup window resizing from being disabled.
scrollbars:  Prevents the scrollbars on a popup from being disabled.
status:  Prevents the status bar from being hidden.
Ignore "status=no" in the window features argument of and prevent popups from hiding the status bar. (Default);
titlebar:  Prevents the title bar from being hidden.
toolbar:  Prevents the navigation toolbar from being hidden.
toolkit. scrollbox. clickToScroll. scrollDelay Integer Determines how many milliseconds to wait before scrolling the tab strip by another increment. (Default: 150)
toolkit. scrollbox. scrollIncrement Integer Determines how many pixels to scroll at a time when scrolling the tab stripís scrollbox. (Default: 20)
toolkit. scrollbox. smoothScroll Boolean True (default): Scroll the tab strip smoothly to a newly-selected tab.
False: Move to the new tab immediately.
view_source. tab_size Integer sets the width of a tab character in the view source window. Already open windows aren't updated (implemented in bug 295506 in trunk builds (mozilla-1.9.3a1) starting 2010-02-03)
Unrelated about:config options of interest
browser. bookmarks. autoExportHTMLBooleanTrue - Export bookmarks to bookmarks.html each time the browser shuts down.
False (default) - Do not export HTML at shutdown.

Will be needed for 3.1 and 3.2 so that Ctrl+Tab, Ctrl+Shift+Tab work browser.ctrlTab.previews removes tab preview
# Set browser.ctrlTab.mostRecentlyUsed to false (create name)
# Set browser.ctrlTab.recentlyUsedLimit to 0

also check these into table
loadDivertedInBackground is for external links, not bookmarks. There's a
loadBookmarksInBackground pref that has UI

How To Modify Hidden Preferences Using about:config[]

How to open everything (url, search, bookmarks) in a new tab with Firefox 3 at x2b4 with JavaScript using userChrome.js instead of having to use Alt+Enter.  Should lead to groups of webpages that invoke Javascript (userChrome.js, etc) hands off similar to how works with styling changes instead of hardcoded in userChrome.css     As interesting this concept is (see comment #41 there), it prevents use of bookmarklets from the location bar and from bookmarks, so is unusable.  Possibly some code in has a solution look for "// It is now possible to disable the JavaScript method" involving
  user_pref("dom.disable_open_click_delay", 1000);

Some settings used and/or found in newsgroups (#settings)

NameMine on 2007-01-22
using Firefox 2.0
Default Multiple Windows
No Tabs (Tab Killer)
One Window
and No Tabs
browser. block. target_new_window (user True) False  
browser. link. open_external (default 3) 3 - New Tab2 - New Window1 - Current
browser. link. open_newwindow (default 3) 3 - New Tab2 - New Window1 - Current
browser. link. open_newwindow. restriction (applies to JavaScript, 0 all into tabs) (default 2)22 1 - like IE for JavaScript
browser. link. open_newwindow. ui     
browser. search. openintab (user true) false  
browser. search. order. (digit)    
browser. tabs. autoHide (user False) false  
Browser. tabs. closeButtons (user 3 at right)    
browser. tabs. forceHide (default false) falseTrueTrue
browser. tabs. loadBookmarksInBackground (default false)false  
browser. tabs. loadDivertedInBackground (default False)false  
browser. tabs. loadFolderAndReplace (user False) false  
browser. tabs. loadGroup (default 1) 1  
browser. tabs. loadInBackground (default False) false  
browser. tabs. loadOnNewTab (default 0) 0  
browser. tabs. opentabfor. bookmarks     
browser. tabs. opentabfor. middleclick (default True) [see mouse]truefalse 
browser. tabs. opentabfor. searchdialog (**used when search bar is hidden)   
browser. tabs. opentabfor. windowopen (obsolete -- user False **)N/A  
browser. tabs. opentabfor. urlbar (obsolete) N/Afalse (obsolete) 
browser. tabs. showSingleWindowModePrefs (default is False, determines whether to display "Single Window Mode" in preferences (see bug 266759) false  
browser. tabs. warnOnCloseOther (default true)tr12ue  
browser. windows. loadOnNewWindow (default 1) 1  
(new tabs in immed before/after or at end) (avail in humongous TMP)   

When you have finished changing your settings, test them out in the Target test area of Tabs page.

Notes on Dummying down of Firefox HELP and significant loss of material in the MozillaZine about:config help.
  1. The actual table from which many entries came from is being hacked away at, so you would have to find the individual entry by itself.  The categories tables such as preferences are a farce because you need to find something not knowing what you are looking for.  This table is probably your best hope of finding TAB configuration entries in context with similar entries.
  2. MozillaZine articles in general are also at risk of being lost to the less helpful material (pablum) at
  3. The Firefox help (F1) has been dummied down for less sophisticated users, such useful Tips and Information that provided Tips on changing userChrome.css, userContent.css, and configuration preferences (about:config) used to be within three clicks of installing Firefox.
Some Developer webpages
  1. Mozilla Cross-Reference mozilla-central mozilla/browser/app/profile/firefox.js, a listing of distributed settings and value settings. (Don't have a clear definition of the file, nor whether to choose the trunk at the top as Firefox or if Firefox 3.6 would be Mozilla 1.9.2)

Page was originally edited by with  Nvu and with Front Page as an experiment, don't like either of them.  Updates are with Notepad like all my other pages, and use of CopyURL+ extension with a 3 column pattern may be used for some additions.

user_pref("copyurlplus.menus.12.copy", "<TR><td><a href=\"%URL_HTMLIFIED%\">%TITLE_HTMLIFIED%</a></td><td>Boolean 
|Integer |String</td><td>%SEL_HTMLIFIED%</td></tr> "); 
user_pref("copyurlplus.menus.12.label", "Tab documentation (3 columns)"); 
The table on this page has been extracted from which is part of the

Modifying configuration entries should be intuitive, but more help is available at

Having trouble with pop-up windows, try these settings:
browser.block.target_new_window defaultbooleantrue user setboolean0
dom.disable_open_during_load user setbooleanfalse
dom.disable_window_flip user setbooleanfalse
dom.disable_window_move_resize user setbooleantrue
dom.disable_window_openuser setbooleantrue
dom.disable_window_open_feature.menubar user setbooleantrue
dom.disable_window_open_feature.minimizable  user setboolean  true
dom.disable_window_open_feature.scrollbars user setbooleantrue
dom.disable_window_status_change.scrollbars user setbooleantrue
dom.event.contextmenu.enabled user setbooleanfalse

Testing of Ctrl+TAB

Revised Ctrl+Tab and All Tabs UI landed, disabled by default.

I've landed bug 465076 today. The UI is now disabled on trunk. This is controlled by the browser.allTabs.previews and browser.ctrlTab.previews preferences. I'd like to encourage nightly testers and whoever's interested to flip both prefs and report bugs, so that we can make further progress there. I've filed bug 505404 for tracking these bugs. (2009-07-21, by Dao)

Firefox/Sprints/Control Tab - MozillaWiki

Finding Preference Related Information (and sorting preferences) (#findprefinfo)

Sorting Preferneces:

You can sort the  about:config  list on any of the columns including the "Status" column, and the secondary order will be alphabetically on "Preference Name".

You can type  about:support  into the location bar to see ONLY changed settings.  Change preferences are in the "Modified Preferences" section, which is in alphabetical order.
For other sections you may have to sort table columns with a bookmarklet or with an extension.
An additional advantage to using the extension is that you can sort first on a minor sort and then on your major sort, the bookmarklet only gives you one column of sorting.

Finding more information about your preferences:

Google search on preferences;
In your  about:config  list, right-click on the preference name (or row) and choose "Prefsearch" -- if you have installed

In your  about:support list  select the preference name, then use built-in search by right-clicking on selection and choosing "Search Google for ...." (uses your default search engine)

Most of the common user assigned preferences are in
if they relate to tabs, I probably have them here on this page, with additional information. (this page)

Summary of my Tab related changes   (#summary)

Check some of the Tab configuration options available for tabs

Extensions   (#extensions)

The Tab extensions that I currently use are simple extensions and should be good from one version of Firefox to another but if one should fail it would be a minor inconvenience compared to those that have choose Tab Mix Plus (xxx) and never know what actually is available in Firefox and better choices of extensions.

You can see my complete InfoLister listing of extensions I have currently installed (some are disabled), and you can find descriptions and usage notes for those and extensions I may have used in the extensions table within Firefox Customization (Notes) where you will find my notes on the following extensions.  The extensions below total 198KB compared to the troublesome Tabs Mix Plus extension (417KB).

about:config       (#aboutconfig)

    about:config user set settings for browser.tabs.*   --   see picture at [2010-01-03]
browser.tabs.closeWindowWithLastTab  booleanfalse
browser.tabs.insertRelatedAfterCurrentbooleanFalse -- will be needed for 3.6

Keyboard Shortcuts   (#keyboard)

Keyword Shortcuts (#kws)

Tab Related Styles at   (#styles)

    Other styles that I use can be found here

Testing of tab related changes (#testing)

This page was created on 2007-01-22, and is a continuation of the targetted link testing on my tabs.htm page look for my email address at the bottom of that page.