New Firefox 49 features in Fedora

The latest release 49 of Firefox comes with some interesting new features. Here’s what they mean for Fedora users and how to enable them beyond default setup.

Make a safe playground

When you’re testing Firefox, you should create a new fresh profile. If something goes wrong, you won’t lose data. The extra profile also allows you to run additional instances at the same time, each with a different configuration.

Open a terminal and create a new Firefox profile:

$ firefox --ProfileManager

Then run your profile:

$ firefox -P profile_name --no-remote

The –no-remote parameter launches an independent instance, instead of connecting to a running one.

Now for the fun part! Type about:config in the location bar to bring up hidden configuration options. The remaining tips in this article require you to edit these configuration keys. All changes usually require you to restart the browser.

Graphics acceleration

Firefox integrates the Skia graphics library as seen in Google Chrome. Unlike Cairo, the former default, Skia promises faster and parallel graphics rendering on Linux.

Skia is not yet enabled completely, but only for canvas HTML5 elements. For a full Skia experience, which may provide anything from ultra-speed to a crash on startup, set to skia.


Electrolysis not only dissolves water but is also meant to speed up Firefox. When Electrolysis is enabled, all web content runs in a separated process under the plugin-container, emancipated from the main browser.

Firefox 49 is a bit picky, and not every piece of content will work this way. To check content status, open the about:support page and look at the Multiprocess Windows row. If some content is not working with Electrolysis, you can try other options to tune the function. A good start is to disable incompatible extensions and set browser.tabs.remote.autostart to true.

For more instructions, including how to force-enable Electrolysis, refer to the Mozilla Wiki.

Dark times are back

At least for your browser, they are. If you like dark themes on the desktop and want the same for the web, toogle widget.allow-gtk-dark-theme to true. Firefox will use a default dark theme for both the user interface and web content.

New in Fedora Using Software


  1. The “Dark times are back” didn’t work on Fedora 24 system up to date (Firefox 49.0 installed).
    The option didn’t exist on about:config page, and if I create this entry then I restart Firefox, nothing happened.

    So, are you sure about this procedure with this specific version?

  2. Steve

    In chemistry and manufacturing, electrolysis is a technique that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Water is often the solvent used with an electrolyte in the process. Basically, it is the decomposition of the constituent elements comprising a particular solution.The electrolysis action does not dissolve water. Interesting enough, it is also a method used to plate things like circuit board copper with silver or gold, or nickle plate the bumper on your crown vic. I’ll check it out in Firefox though, to see what it actually does, since emancipation is not segregation but a proclamation for unification.

  3. … you can used your skills to make settings into firefox.
    also this: about:debugging … and many features can help you to see what happens with your firefox.

  4. Hrafnkell Brimar Hallmundsson

    I can’t find the widget.allow-gtk-dark-theme boolean in about:config, and adding it manually did not do anything.

  5. toogle widget.allow-gtk-dark-theme to true

    Where? Unavailable in about:config.

  6. Matt Shindala

    If you like dark themes on the desktop and want the same for the web, toogle widget.allow-gtk-dark-theme to true.

    I think you mean “toggle”.

  7. wigust

    Still have a video tearing compare to chromium or chrome on

    • Artem

      Set “true” for “layers.acceleration.force-enabled” in “about:config” and no tearing at all.

    • Sebastiaan Franken

      That might be your graphics drivers. Or maybe Flash. Is Firefox using HTML5 video playback or the old Flash plugin?

  8. Shawn

    widget.allow-gtk-dark-theme was not present in about:config, I created the boolean, set it to true, and it’s still light. Toogle…lol.

  9. Shawn

    widget.allow-gtk-dark-theme to true is not present, I created the boolean myself and set it to true and nothing changed-toogle LOL

  10. Good. Thanks for informing Stransky.

  11. Rubén

    I’ve just upgraded Firefox to v49 and I can’t find “widget.allow-gtk-dark-theme “. I use Gnome dark theme 🙁

  12. darky

    Strange, I have set widget.allow-gtk-dark-theme to true, but the UI Elements are still light gray. I have the standard theme installed + some addons (relevant ones seem to be gnotifier + htitle). Am I missing something?

  13. max

    The dark theme does not yet work with Fedora 24 Gnome 3.20.4 and Firefox 49. What am I missing?
    I created the about:config Boolean and set it to true. Dark GTK Theme globally enabled via gnome-tweak-tool
    Many Thanks

  14. batisteo

    But I don’t find the parameter widget.allow-gtk-dark-theme in about:config. I did something wrong?

  15. Alex

    “toogle widget.allow-gtk-dark-theme to true. Firefox will use a default dark theme for both the user interface and web content”

    How do you do that ?

    Thank you

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