Firefox

USE flags

The above list of USE flag is not comprehensive. Use equery (part of app-portage/gentoolkit) for a full list:

Emerge

To compile the source version of Firefox ESR, issue:

Be aware that non-ESR versions are not getting stabilized.

Emerging the source version of Firefox can be a long process; a pre-compiled (binary) version does exist in the Gentoo repository, however users of the pre-built package should note the warning below and this message. To emerge the Firefox binary, issue:

Running under Wayland

Since Firefox 65, it is possible to run Firefox natively under Wayland by launching it with the GDK_BACKEND=wayland environment variable set after having emerged Firefox with the USE flag wayland enabled. From a terminal:

To set Firefox to always open using the Wayland backend, set the following environment variable in the user's shell. Bash is the default user shell on Gentoo systems:

<syntaxhighlight lang="bash"># Enable Wayland support for Mozilla Firefox
export MOZ_ENABLE_WAYLAND=1</syntaxhighlight>

Enabling multitouch

Middle mouse scroll (autoscroll)

Traditionally in Linux, the middle mouse button is used to paste the currently selected (highlighted) text into a text field. On Windows systems, the middle mouse button in Firefox is used for click-and-drag scrolling up and down the page. This functionality can be enabled in Firefox by opening about:config and setting the following value^[1]:

• general.autoScroll = true

Middle click-and-drag scrolling should now be enabled.

Although not necessary, sometimes it is desirable to disable all other middle-click functionality within Firefox when using click-and-drap scrolling. Open about:config and set the following values to disable middle-click functionality:

• middlemouse.contentLoadURL = false
• middlemouse.openNewWindow = false
• middlemouse.paste = false

Threads

Firefox >= 54 has 4 threads enabled by default. Threads can be adjusted by modifying the following in the about:config interface:

Where N is an integer number.

Audio backend

Firefox's cubeb audio library supports a number of different backends^[2][3].

Disabling percent-encoding

Normally, URLs that are copied from the address bar get percent-encoded. This may cause an annoyance when certain non-Latin symbols (such as Cyrillic) get encoded, as they become unreadable to humans.

To disable percent-encoding when copying from the address bar, set the about:config option network.standard-url.escape-utf8 to false.

Disable enforced digital signatures verification in Firefox >=48

This concerns mandatory add-ons signature in Firefox and can lead to security issues.

<syntaxhighlight lang="javascript">//
try {
  Components.utils.import("resource://gre/modules/addons/XPIProvider.jsm", {})
    .eval("SIGNED_TYPES.clear()");
}
catch(ex) {}
END</syntaxhighlight>

<syntaxhighlight lang="javascript">pref("general.config.obscure_value", 0);
pref("general.config.filename", "config.js");</syntaxhighlight>

<syntaxhighlight lang="diff">--- a/build/mozconfig.common.override 2017-02-06 14:26:05.891721140 +0900
+++ b/build/mozconfig.common.override 2017-02-06 14:25:41.115763755 +0900
@@ -9,3 +9,4 @@
 # to override anything done previously.
 #
 # The common expected usage is for try builds with nondefault options.
+MOZ_REQUIRE_SIGNING=0</syntaxhighlight>

<syntaxhighlight lang="diff">diff --git a/browser/confvars.sh.old b/browser/confvars.sh
index 7637236..2264bf5 100755
--- a/browser/confvars.sh.old
+++ b/browser/confvars.sh
@@ -27,7 +27,16 @@ fi
 # Enable building ./signmar and running libmar signature tests
 MOZ_ENABLE_SIGNMAR=1
 
-MOZ_SAFE_BROWSING=1
+# Disable 'safe' browsing
+MOZ_SAFE_BROWSING=0
+# Disable checking that add-ons are signed by the trusted root
+# https://github.com/mozilla/positron/blob/master/build/mozconfig.common
+MOZ_ADDON_SIGNING=0
+# Disable enforcing that add-ons are signed by the trusted root
+MOZ_REQUIRE_SIGNING=0
+# https://dxr.mozilla.org/mozilla-central/rev/5cf4d2f7f2f2b3df2f1edd31b8bdce7882f3875c/browser/confvars.sh
+# https://dxr.mozilla.org/mozilla-central/source/browser/confvars.sh
+
 MOZ_APP_VERSION=$FIREFOX_VERSION
 MOZ_APP_VERSION_DISPLAY=$FIREFOX_VERSION_DISPLAY
 MOZ_EXTENSIONS_DEFAULT=" gio"</syntaxhighlight>

Special URLs

Firefox includes a few dozen special URLs that can be helpful in determining more information about various Firefox settings. These URLs can be entered into the Super Bar (via copy and paste) to view the special pages. A few of the more significant ones include:

• about:addons - Page for managing extensions.
• about:buildconfig - Page containing build information about the currently running version of Firefox. Use this page to check what compiler flags were set during Firefox's build.
• about:cache - Information about the Network Cache Storage Service.
• about:config - Modify internal browser settings and preferences.
• about:memory - Measure and show memory reports, free memory, etc.
• about:networking - Analyze current network information such as HTTP, socket, and DNS connections.
• about:plugins - List installed plugins such as Widevine Content Decryption Module (DRM software).
• about:support - A page containing technical information that might be useful when trying to solve a problem. Includes information on WebGL, Window Protocol (X11 or Wayland), and compositing graphics backends.
• about:telemetry

Finally, about:about will display the whole list of Firefox' “about” pages. A description for each page is available at Firefox and the "about" protocol.

See also Firefox chrome:// document URLs.

XDG integration

In order to make Firefox use XDG file associations set Content Type's Action to /usr/bin/xdg-open

• 
  Firefox file associations

To ensure Firefox is being used by other applications for handling HTTP and HTTPS links, run the following commands:

Running under KDE

Firefox is built with GTK, and by default will use the GTK file picker. To enable the KDE file picker, install kde-plasma/xdg-desktop-portal-kde, which is installed by default if kde-plasma/plasma-meta is installed. After that set widget.use-xdg-desktop-portal to true in about:config.

Running in sandbox

The Simple sandbox article explains why »Sandboxing Firefox is mandatory«.

SSL/TLS security enhancements

Some about:config SSL/TLS security options which are not defaults (as of Firefox 52.2.0) that increase the security of HTTPS connections are listed below. Two of them rarely break access to websites.

Safer browsing with add-ons

Firefox has a massive community behind it and a result many add-ons have been created to aid with specific interests of users. Many users are concerned about their privacy (tracking, bubbling, targeting, etc) while web browsing. Installing Add-ons can aid in adding an extra level of privacy to their browsing.

The add-on menu can be accessed by navigating the following menus: Hamburger button (top right under the X) → Add-ons

gtk+:3 pulls in DBUS

Since version ≥53.0, Firefox has dropped gtk+:2 support urging Larry to use gtk+:3. This, however, by default, pulls-in annoyances like DBUS. This can be avoided by using a patch from BSD available in bug #669234 or the mv overlay.

Please note that, when running Firefox under native Wayland (i.e. not using XWayland), Firefox will implicitly try to use DBus to enable its remote control feature and crash, likely with a segfault, due to the lack of DBus. Thus, it is necessary to invoke Firefox with the --no-remote command-line argument or MOZ_NO_REMOTE environment variable set (to anything).

Crashes

If Firefox crashes for no apparent reason every few minutes with an error message like ABORT: X_GLXDestroyContext: GLXBadContext; 15 requests ago it might help to add the Firefox user(s) to the video group:

Latest adobe-flash-23 does not work

It is possible to use PPAPI NPAPI plugin adapter. For more info read here

Lack of sound (www-client/firefox)

If Firefox built with the gstreamer USE flag does not play sounds, and some web sites tell you to install Flash to play music, make sure that the necessary codecs are installed:

Lack of sound (www-client/firefox-bin)

www-client/firefox-bin expects PulseAudio. Alsa-only systems might work around this limitation by using media-sound/apulse. For this to work you'll need to modify Firefox sandbox settings by going to about:config and adding "/dev/snd/" (note the trailing slash) to "security.sandbox.content.write_path_whitelist" option.

If you're storing ALSA settings in /home, also, be sure to add "/home/<username>/.asoundrc" to the "security.sandbox.content.write_path_whitelist" option. Whitelist path could be separated by comma.

Since around Firefox 58 there is additional modification needed to work around seccomp sandbox: security.sandbox.content.syscall_whitelist = 16

Now you can go ahead and create alias for running firefox through apulse:

Screen tearing / stuttering smooth scrolling

Build www-client/firefox with USE flag hwaccel. See the mentioned Mozilla bug for background information.

Green video screen (youtube)

If disabling (graphics) acceleration in settings does not work, disabling the equivalent options under about:config like layers.acceleration.force-enabled (85.0) might.