Advanced Firefox Configuration

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  • DevynCJohnson
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    • @devyncjohnson

    Firefox is a popular OSS web-browser for Linux, Android, Windows, OS X, and many other operating systems. Many users like to customize Firefox to their needs. Interestingly, Firefox has a registry that users can edit to further customize Firefox. To access this registry, type "about:config" in the address bar. Be careful when editing options in this registry. Incorrect configuration can cause problems. Thunderbird also has this registry system, but Firefox will primarily be discussed in this article.


    The registry interface has a search-bar that users can use to find an entry. The search-bar accepts REGEX (wildcards). The entries can be sorted by Name, Status, Type, and Value. Only the "Value" can be changed. The value is one of three types - string, integer, and boolean. A string is a set of text/characters. An integer is a non-decimal number. Booleans are either "true" or "false". The "Status" column indicates if the value is set to the default (indicated by "default") or changed by the user ("user set"). Entries changed by the user are in bold. These entries may have been changed by the user in the "Preferences" or through the registry interface or by an add-on.

    The entries use names in the form "Category.Name" or "Category.Subcategory.Name". Many categories exist and add-on may create their own categories. Some of the main categories are listed below.

    • accessibility
    • advanced
    • alerts
    • app
    • bidi
    • browser
    • config
    • content
    • Dom
    • editor
    • extensions
    • font
    • geo
    • general
    • intl
    • javascript
    • layout
    • mail
    • mailnews
    • middlemouse
    • mousewheel
    • network
    • news
    • nglayout
    • plugin
    • print
    • privacy
    • profile
    • security
    • signon
    • snav
    • toolkit
    • ui
    • update
    • update_notifications
    • view_source
    • xpinstall


    The accessibility entries allow users to customize the accessibility features.


    This category only contains two entries (advanced.mailftp and advanced.system.supportDDEExec). "advanced.mailftp" holds a boolean value that indicate whether or not the password used for mail is used for FTP anonymous logins. "advanced.system.supportDDEExec" holds a boolean value for setting (or not setting) DDE-related subkeys. A value of "true" will make Firefox at like a DDE server. This means HTTP messages meant for http-handling are interpreted by Firefox. The default value is "true".


    This category contains three entries - alerts.slideIncrement, alerts.slideIncrementTime, and alerts.totalOpenTime. These control certain aspects of the time sliders (as seen in the "Downloads").


    These entries control application updates.


    The direction of the text is controlled with these entries. "bidi" stands for "Bi-Directional". Also, the character-set and numeral type can also be changed with these entries.


    Many entries and subcategories belong to the "browser" category that changes the browser's behavior.


    The "camera" category is seen on devices with a webcam or some type of video-input hardware. Users can edit various interactions between Firefox and the camera.


    This category has three entries - config.trim_on_minimize, config.use_system_prefs, and config.use_system_prefs.accessibility. "config.trim_on_minimize" holds a boolean value that allow or disallow MS-Windows to trim the memory used when Firefox is minimized. "config.use_system_prefs" holds a boolean value that indicates whether or not Firefox will use some of the system's settings (like for accessibility and proxy settings). "config.use_system_prefs.accessibility" is just like the previous entry, but this is specifically for accessibility.


    These entries control the rendering of webpages.


    The "datareporting" category pertains to the Firefox "Health Reports" and other related features.


    The "device" category controls hardware access such as storage and sensors.


    The "devtools" category controls various debugging and developer tools.


    These entries control certain properties and behaviors of the Document Object Model (DOM). DOM refers to the portable way of using and manipulating various markup-languages such as XML, HTML, and others.


    These entries control the composer. The composer is used for fields/boxes that accept text such as email. This category mainly pertains to Thunderbird.


    Many addons place their registry entries under the "extensions" category.


    These settings control the font sizes and types.


    The "gecko" category is similar to the "NGLayout" category.


    This category has two entries - geo.enabled (for location awareness) and geo.wifi.url (the geolocation service provider).


    This category is like the "browser" category, but this one is more general.


    The graphical effects can be tweaked with the "gfx" category.


    Various html5 properties can be edited with the "html5" entries.


    Various international settings are controlled here such as character-sets and keyboard mapping.


    JavaScript options and controls are found here such as memory management, the console, REGEX, and more.


    The page layout, CSS, spell checking, and other objects are controlled with the "layout" entries.


    (Thunderbird only)

    Email capabilities are managed with the "mail" category.


    (Thunderbird only)

    RSS and other forms of news and information updates are controlled with these entries.


    Various key-presses associated with a middle mouse button can be customized here.


    Various key-presses associated with a mouse-wheel button can be customized here.


    Network connection, security, proxy, cookie, DNS, and other options are controlled here.


    (Thunderbird only)

    RSS and other forms of news and information updates are controlled with these entries.


    NGLayout (Next Generation Layout Engine), or the Gecko engine, processes XUL, CSS, JavaScript, and HTML. These entries allow the user to make changes to the Gecko engine's functioning and debugging.


    The plugins (not addons), like Flash Player, have their settings under "plugin".


    These entries control printing (both physical and virtual) and the print preview.


    The privacy settings include cache control, popups, history, offline data, etc.


    The profile manager can be tweaked with these entries.


    Users can edit the security settings such as SSL, RSA, TLS, etc.


    All of the auto-fill features are configured with these entries.


    Spatial Navigation (Snav) features can be tweaked with these entries. Snav is used to change the focus of the webpage. (


    The zoom feature (ctrl++ and ctrl+-), text searching, and tab-scrolling can be edited with these entries.


    The User Interface entries control the keyboard shortcuts and other types of interactions with Firefox. The color used when selecting/highlighting text can be edited in the "ui.textSelectBackground" entry.


    The frequency of update-checks and other update options can be changed here.


    The notifications associated with updates can be configured here.


    "View Source" refers to the viewer used to display a page's source code. This viewer can be configured here.


    Firefox addons are files with the "*.xpi" extension. All of the entries in the "xpinstall" category are used to tweak the features associated with tweaking the addon installation system.

    Many other categories are available, but these are the more common categories. Others (like "svg") contain one entry (svg.enabled).

    Notice that many of these categories overlap in some areas. Also, some of these categories may be seen in some devices but not others (like "geo").

    Having a basic understanding of this registry system helps users to figure out how to better customize Firefox and other Mozilla-related software.

    Further Reading

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