Original author: Tommy Nguyen

Last modified: Mon Aug 1 17:02


The recommended way of managing config settings nowadays is arkenfox. Help can be found in the wiki.

For historical purposes, advice on individual settings can be found below. Note however that these settings may be deprecated or inactive in the future.

Disable automatic redirect to a website if typing an invalid URL

Example, you type firefox build/html/fedora/gcc.rst (where gcc.rst doesn’t exist) and it opens up Go to about:config and set browser.fixup.alternate.enabled to false.

Glitchy UI when using custom GTK theme

If you are using a custom GTK theme for your window manager, you need to instruct Firefox to use the default theme. On XFCE, this will be something like:

env GTK_THEME=Adwaita:light firefox

If that’s inconvenient, you can add the change to Firefox directly. Go to about:config and add a new key called widget.content.gtk-theme-override. Set the value to Adwaita:light or whatever you prefer.

Forcing dark theme

By default, Firefox will use your system preference to determine whether or not to use a dark theme, but does not expose this option. In about:config, create a new entry called ui.systemUsesDarkTheme and set it to 1.

If you experience a “flashing” white background when loading a new tab, then you need a custom userContent.css file. First, enable toolkit.legacyUserProfileCustomizations.stylesheets. Then create a chrome folder in your user profile and populate userContent.css with the following contents:

   dark background in new tabs without a white flash (with tridactyl newtab)
:root {
  --tridactyl-bg: #1d1b19 !important;
  --tridactyl-fg: white !important;

    set the background color of the new tab page (without tridactyl or with tridactyl without newtab)
@-moz-document url-prefix(about:home), url-prefix(about:newtab) {
  body {
    background: #1d1b19;

    if you set it straight to body element, it will be applied to the random web pages
    that don't explicitly set the background color of their body element
    (there's many of those online)
/* body { */
/* background-color: #1d1b19; */
/* } */

Credit goes to @maricn for the CSS.

Disable network.http.referer.spoofSource

Some privacy guides or tools suggest you enable this setting. However, it can break websites. This article suggests using setting network.http.referer.XOriginPolicy and network.http.referer.XOriginTrimmingPolicy to 2 instead.

Minimizing ram usage

Firefox uses multiple processes for tabs which can lead to increased RAM usage over time. While you can go to about:memory and run the garbage collector, it has a marginal effect. Restarting the browser is needed to keep RAM usage down. However, there are two things you can do to mitigate high RAM usage:

  • in about:config, set browser.newtab.preload to false. This will prevent tabs from loading until you click on them

  • Install Auto Tab Discard which will put tabs to sleep automatically if not in use

Alternative to Stylus

If you wish not to have Stylus installed but want to replicate its functionality, here’s what you can do. First, go to each style you have installed and export it. It will look something like:

@-moz-document domain("") {
    /* insert style here */

You can use url-prefix, etc. Put it in a folder somewhere. We want to now append this to userContent.css which is going to be located in the chrome folder in your Firefox profile.

for file in *.css
    cat "$file" >> $HOME/.mozilla/firefox/some-profile.default/chrome/userContent.css