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Switch between Dark and Light Themes in Firefox Nightly on the fly

The Developer edition of the Mozilla Firefox browser comes with a different, dark theme. I discovered a trick which will allow you to switch between dark and light themes for Firefox Nightly builds. After you follow the instructions in this article, you will be able to switch between the regular and dark theme via the Customize mode of Firefox.

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Note that this trick only works in the Nightly version of the Firefox browser. You might need to download it. Here is where you can get it.
  1. Point your browser to the following link:
    firefox-37.0a1.en-US.win64-x86_64.zip (here is the Win32 build for 32-bit Windows users). This is the latest Firefox Nightly version available for Windows as of this writing. You can also check out the latest-trunk folder on Mozilla's ftp server to always get the most up-to-date win64/win32 Nightly build of Firefox.
  2. Unpack the downloaded archive to any folder you like. In my case, I will use the C:\App\Firefox-nightly folder:
    firefox nightly dark theme
  3. Create a new dedicated profile folder for the Nightly build. For example,
    C:\App\Firefox-nightly\profile

    We need this folder to prevent the Nightly build from messing up your regular Firefox profile.

  4. Create a new shortcut on your Desktop with the following command:
    C:\app\firefox-nightly\firefox.exe -no-remote -profile C:\app\firefox-nightly\profile

    This will allow you to launch the Firefox Nightly simultaneously alongside the stable Firefox version. It will also use the profile directory we just created above.
    firefox nightly new shortcut

Correct the paths to match folders you are using if you used some other folder path instead of C:\app.. and you are done.

Now do the following:

  1. Open a new tab and enter the following text in the address bar:
    about:config

    Confirm that you will be careful if a warning message appears for you.

  2. Enter the following text in the filter box:
    browser.devedition.theme.showCustomizeButton

    showCustomizeButton

  3. You will see the parameter browser.devedition.theme.showCustomizeButton. Set it to true.
    showCustomizeButton true
  4. Press F12 to open Developer tools:
    developer tools
  5. Click the Options icon (the gray gear icon on the right) and pick the Dark theme:
    nightly developer tools
  • Now click the Sandwich menu button and then click Customize. You will notice the "Use Developer Edition theme" button at the bottom:
    use developer edition theme button
  • Click that button and enjoy the dark theme in your Firefox Nightly:
    firefox nightly dark theme in action
  • That's it. Now you will be able to quickly switch between dark and light themes in Firefox Nightly on the fly via the "Use Developer Edition theme" button!

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    Author: Sergey Tkachenko

    Sergey Tkachenko is a software developer who started Winaero back in 2011. On this blog, Sergey is writing about everything connected to Microsoft, Windows and popular software. Follow him on Telegram, Twitter, and YouTube.

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