Firefox Tweak Guide
[Page 10] Advanced Tweaking (Pt.2)
About:Config Preferences
This section contains the instructions on how to conduct advanced preference tweaking in Firefox using the About:Config method, as mentioned on the previous page. This is the most common way to perform advanced tweaking in Firefox, as it provides access to the widest range of preferences. To view and alter these preferences, you must first go to your Firefox Address Bar and type "About:Config" (without quotes), then press Enter. You will be a shown a warning which you should accept, and then you will see a large listing of preferences sorted alphabetically.
There are three main types of preference variables shown here: Integers, Boolean and String variables. An Integer preference can only take a whole number value; Booleans can only take True (on) or False (off) values; and Strings can consist of any combination of text and numbers. You can change the value of any preference quickly by double-clicking on it: Booleans will toggle from True to False and back; Integers and Strings will open a dialog box which allows you to input a new value. Or you can right-click on a preference and select Modify or Toggle as relevant.
Before making any changes here, make sure you have read the information on the previous page, and importantly, Please read all of the notes further below carefully before tweaking your About:Config
Note: Aside from About:Config, there are also other About: commands you can use, such as About:Cache and About:Plugins to show you more information about your current build of Firefox - details of all of these are here.
Important Notes on About:Config:
To make sure your preference changes are saved and to test the effects of preference change(s), close all open Firefox windows and restart Firefox.
Preference Format
The preferences list below is presented in alphabetical order with the full name in italics, the preference type (i.e. Integer, Boolean or String) in [ ] square brackets, any recommended values in ( ) round brackets, whether it needs to be created *Create, and then followed by a brief description. Recommendations are only given for a few of the settings - most will require you to experiment as the choice is often based on personal taste and/or your specific hardware and OS environment settings.
accessibility.typeaheadfind.casesensitive [Integer] - If set to 0, searches using the 'Find as you type' feature are not case sensitive, if set to 1 they are case sensitive.
accessibility.typeaheadfind.enablesound [Boolean] (False) - By default this is set to true, which means the 'Search for text when I start typing' feature makes a noise each time you enter characters in a string which is not found on the current page. To turn this annoying sound off, set this option to False.
accessibility.typeaheadfind.linksonly [Boolean] - If set to true, this setting makes the 'Find as you type' feature search only for links on a page.
accessibility.typeaheadfind.soundURL [String] - Determines the sound made when the 'Search for text when I start typing' feature doesn't find a match. The default is beep, but it can be set to a blank value to disable sounds, or set to the full path to a .wav file which it will play in place of the beep.
accessibility.typeaheadfind.timeout [Integer] - Sets the amount of time before the 'Search for text when I start typing' feature search box disappears from the screen when inactive. The value is in milliseconds, so 5000 = 5 seconds for example. Lowering it will close the box more quickly when inactive.
alerts.totalOpenTime [Integer] (2000) - Determines for how many milliseconds to show the 'Download complete' or 'Updates Available' alerts. I recommend reducing this to 2 seconds (2000).
app.update.interval [Integer] - If you've enabled automatic checking for Firefox updates in the Options menus, this setting determines how many seconds Firefox will wait between checking for updates (at the URL contained in the app.update.url preference). The default is 24 hours (86400 seconds).
browser.bookmarks.livemark_refresh_seconds [Integer] *Create - This is the number of seconds Firefox waits between checking for updates to any Live (RSS) Bookmarks you may have. The default is 3600 seconds = 1 hour, and for most purposes this is fine.
browser.backspace action [Integer] - Determines what the Backspace key does in Firefox - by default it goes back a page when pressed (a value of 0); if set to 1, it will scroll up the page when pressed; if set to 2 or above, it will be disabled.
browser.bookmarks.autoExportHTML [Boolean] - By default Firefox creates 5 bookmarks backups in .JSON format - see previous page for details. If this setting is set to True, Firefox will start backing up bookmarks in .HTML format instead.
browser.bookmarks.max_backups [Integer] - By default Firefox creates 5 bookmarks backups in .JSON format - see previous page for details. The number of backups created is controlled by this setting; a value of 0 disables backups, while -1 will remove the limit on the number of backups allowed.
browser.cache.check_doc_frequency [Integer] (3) - This setting determines how often Firefox checks the page you're viewing against the cached version it holds. By default (a value of 3), Firefox automatically checks and only reloads the page if it seems outdated; a value of 2 will never check and always load the cached version (not recommended); a value of 1 will always check for a newer version of the page; a value of 0 only checks once per session. In most cases the default is fine, however if you want to force Firefox to reload new versions of every page you visit, set this option to 1, though this will slow down browsing. Remember you can manually force reload any page at any time by pressing CTRL+F5 if you think you're viewing the outdated version.
browser.cache.disk_cache_ssl [Boolean] (False) - If set to true, this setting allows the caching of secure web pages in your browser cache. This speeds up loading of commonly-visited secure pages, but is an obvious security risk and for that reason it is generally recommended you keep this at False.
browser.cache.memory.capacity [Integer] *Create - This setting determines whether Firefox uses system RAM to cache data, improving performance. A value of 0 turns off caching into RAM, which is not recommended as it can slow down browsing. The default value of -1 tells Firefox to automatically determine the size of the cache based on your physical RAM. In Firefox 3.0 and newer, systems with 512MB of RAM will result in a 14MB cache, 1GB of RAM results in a 18MB cache, 2GB of RAM gives 24MB of cache, and 4GB of RAM or higher results in 30-32MB of RAM cache. The default of -1 should be fine for all people, but if you notice Firefox increasing its memory usage, you can manually restrict this value to a particular amount by entering a value in KB (e.g. a value of 18432 = 18MB).
browser.cache.memory.enable [Boolean] (true) - This setting works in conjunction with the browser.cache.memory.capacity setting above. If set to True, Firefox will use the value specified in the browser.cache.memory.capacity setting to determine how much RAM to use. If set to False, Firefox will not use any RAM to cache, resulting in a performance drop. I recommend setting this to True for all systems unless troubleshooting a potential memory-related problem in Firefox for example.
browser.cache.offline.capacity [Integer] - Web applications can be stored locally for offline use. This setting determines the maximum amount of space they can take up in the offline cache. The default value of 512000 in kilobytes corresponds to 500MB. In general there's no need to alter this as it will only be used if you install an offline web application. If you wish to turn off the offline cache altogether, set the browser.cache.offline.enable setting to False.
browser.cache.disk.parent_directory [String] *Create - Determines the path to the parent directory for the Firefox cache, usually held under your profiles directory (i.e. under "%APPDATA%\Mozilla\"). By specifying a new path here you can move the cache to another drive or partition, which may improve performance or enhance privacy. Note that if this value is being set directly in Prefs.js or User.js, the path requires double backslashes for every backslash instead of single ones (e.g. C:\\ instead of C:\ ).
browser.chrome.favicons [Boolean] (true) - This setting determines the display behavior of the small site icons (usually called 'favicons') visible next to bookmarks and site URLs in the Address Bar. If set to True, these are downloaded and displayed; if set to False they are not. Turning off favicons may increase the responsiveness of the Bookmarks menu, but generally they are best left enabled for easier site identification.
browser.chrome.image_icons.max_size [Integer] - Determines the maximum size in pixels beyond which a thumbnail of an image won't be shown in a tab; higher values can reduce performance. If you don't want thumbnail images shown in tabs at all, set this to 0.
browser.chrome.toolbar_tips [Boolean] - If set to True, small 'tooltips' (popup boxes with descriptive text) will be shown when you hover over items in your Firefox toolbar, as well as on certain objects in some webpages. If you don't like tooltips, set this value to False, but remember this may also disable useful descriptive tooltips on certain webpages.
browser.display.show_image_placeholders [Boolean] (False) - If set to True, image placeholders will be shown until images on a page are fully loaded. If set to False, these are not shown. I recommend setting this to False for a cleaner look as pages load.
browser.download.manager.flashCount [Integer] - This setting determines the number of times the Download Manager will flash in your Taskbar when a download is underway and the Download Manager is not visible - by default it's twice. You can set it to 0 to disable it, or you can raise the value to increase the number of flashes if you really want it to get your attention.
browser.download.manager.openDelay [Integer] (2000) - The value here determines how many milliseconds of delay there will be before the Download Manager window opens at the start of a download. By default the Download Manager window opens immediately (0 milliseconds delay), however you might like to try a value such as 1000 or 2000 (1 or 2 seconds delay) so that for very small downloads you don't have to see the Download Manager window at all, yet the file will still be downloaded as usual.
browser.download.manager.quitBehavior [Integer] - The Download Manager can pause and resume files which are being downloaded when Firefox is closed. By default (a value of 0) an active download will be automatically paused when Firefox closes, and resumed when it next opens. However you can set this to a value of 1, forcing active downloads to pause, but not automatically resume when Firefox starts up again; or set it to a value of 2 so that all active downloads will be cancelled when Firefox is closed.
browser.download.manager.resumeOnWakeDelay [Integer] - The Download Manager resumes any active downloads when started, and this option determines the length of time in milliseconds before a download is resumed after the PC has woken from Sleep mode. You can shorten the value if your network connection is quick to recover when waking from sleep, or lengthen it to ensure the connection is active before Firefox attempts to resume.
browser.download.manager.scanWhenDone [Boolean] - When a download is completed, and if this value is True, it will trigger an automatic scan of the download using your resident Antivirus package. However this can add a bit of time to finalizing a download, especially large downloads, so set this to False if you wish to skip this scan, but make sure to scan any suspicious or untrusted downloads with several malware scanners regardless.
browser.download.manager.showAlertInterval [Integer] - This setting determines for how many milliseconds the "Download Completed" alert is shown when you complete a download. Default is 2 seconds (2000 milliseconds). If you want to disable the download completed alert altogether, set the browser.download.manager.showAlertOnComplete preference to False, though this isn't recommended.
browser.enable_automatic_image_resizing [Boolean] - If set to True (the default), images opened separately will be automatically resized to fit the screen, and will need to be left-clicked to be shown at full size. If set to False they will always be shown at their full size.
browser.fixup.alternate.enabled [Boolean] - If set to True (the default), if a web address is entered in the Address Bar without an appropriate prefix or suffix, Firefox will automatically add them in. For example if you enter http://tweakguides into the Address Bar, Firefox will add www. and .com to either side of the tweakguides text before executing the address. Setting this to False prevents that behavior, and alternatively you can also edit the prefix and suffix used by altering the text in the browser.fixup.alternate.prefix and browser.fixup.alternate.suffix preferences.
browser.fullscreen.autohide [Boolean] - If set to True (the default), when you activate Fullscreen Mode in Firefox (press F11), the toolbars and tab bar will automatically be hidden after a second. If set to False, they won't become hidden and will always be visible.
browser.link.open_newwindow [Integer] - This setting determines where hyperlinks which would normally open in a new browser window end up opening. If set to 1, they open in the current Firefox window; if set to 2 they open in a new window; and if set to 3 (the default) all such links open in a new tab in the current Firefox window. Note that this setting is the same as that found under the in-browser Options>Tabs screen, however there is an additional choice here (setting it to 1).
browser.link.open_newwindow.restriction [Integer] - This setting determines how new windows launched by javascript (usually popups) are treated. If set to 0, all such windows are opened as tabs in the current window; if set to 1 they open as new windows; and if set to 2 javascript windows will be treated like any other opened link unless they have strict values set.
browser.safebrowsing.provider [String] - There are a range of settings here which hold the details of the URLs to be used for reporting and comparing potential malware and phishing sites to Google's Safe Browsing servers. If you wish to retain some level of malware and phishing protection, but don't want data reported back to Google, you can attempt to set all the web address to blank, however this is not recommended.
browser.search.openintab [Boolean] - If set to True, the result of any searches made using the Search box in the toolbar will be shown in a newly opened tab; if set to False (the default), the search results will be shown in the current window.
browser.sessionhistory.max_total_viewers [Integer] - This option determines how many pages to store in memory to speed up the back and forward buttons in Firefox. The default of -1 automatically determines the amount based on your system RAM, and is generally recommended. At 512MB of RAM, 5 pages are held in memory, while 1GB or more of RAM holds 8 pages. You can set this value to 0 to hold no pages in RAM (only recommended for very low RAM or troubleshooting purposes), or increase the value if you often use the back and forward functions for more than 8 pages.
browser.sessionstore.max_tabs_undo [Integer] - Under the History menu in Firefox there is a 'Recently Closed Tabs' item which allows users to select from a list of recently closed tabs to reopen. The default in Firefox 3.5 is a history of 10 recently closed tabs, however here you can change the value to increase or decrease the number held, though it is not recommended that you set this to a high number.
browser.sessionstore.max_windows_undo [Integer] - Under the History menu in Firefox there is a 'Recently Closed Windows' item which allows users to select from a list of recently closed Firefox windows to reopen. The default in Firefox 3.5 is a history of 3 recently closed windows, however here you can change the value to increase or decrease the number held, though it is not recommended that you set this to a high number.
browser.tabs.closeButtons [Integer] - This setting controls how the 'x' close buttons on tabs appear in Firefox. A value of 0 only displays the close button on the active tab; 1 (the default) shows it on all tabs; 2 results in no close buttons being shown at all; and 3 displays a single close button at the end of the tab bar.
browser.tabs.closeWindowWithLastTab [Boolean] - By default as of Firefox 3.5 if you close the last open tab on the screen, it will close the Firefox window altogether. If this setting is changed to False, closing the last tab will instead leave Firefox open.
browser.tabs.forceHide [Boolean] - If set to True, your tab bar will be hidden regardless of how many open tabs you have in Firefox. This is only recommended if you absolutely need every last inch of vertical viewing space.
browser.tabs.opentabfor.middleclick [Boolean] - If set to False, clicking the middle mouse button on a link will not open that link in a tab. This is counter to the default behavior of Firefox, and would only be recommended if you strongly object to middle click opening a tab for some reason.
browser.tabs.tabclipWidth [Integer] - Determines the minimum width of a non-active tab in pixels before a red 'x' close button appears. The default is 140, and raising this value increases the likelihood that a close button won't appear on the tab. If you want to get rid of close buttons altogether you should consider using the browser.tabs.closeButtons preference above.
browser.tabs.tabminWidth [Integer] - As more tabs are opened, Firefox shrinks each tab's width. This setting controls the minimum width a tab can be, with the default being 100 pixels. Raising this value prevents tabs from being too "squished", but means less tabs can be displayed at any one time on the screen (the remainder are shown in the tabs drop down box at the far right of the tab bar). If you want you can also change the browser.tabs.tabMaxWidth value if you wish to change the maximum width of a tab as well from its default of 250 pixels.
browser.urlbar.clickSelectsAll [Boolean] - When set to True (the default), left-clicking once in the Address Bar automatically highlights all of its contents. If set to False, clicking in the Address Bar will only place a cursor where you click without highlighting any text first.
browser.urlbar.maxRichResults [Integer] - This setting determines the maximum number of results shown in the Awesome Bar. The default is 12, but if you find that excessive you can lower the value here. A value of 0 will completely disable the Awesome Bar's functionality.
browser.zoom.siteSpecific [Boolean] - In conjunction with Firefox's full page zooming capability, this setting determines whether your zoomed in/out view applies to an entire site (when set to True, the default), or if it only applies to the currently viewed page (when set to False).
The next page continues the alphabetical listing of About:Config Preferences.
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