Installation

Running classic (pre-Nova) Firefox?

From release 3.0 onward, FoxOne targets the Nova UI. The stylesheet is dual-written (Proton & Nova) and should still work, but it is no longer tested. For a known-good classic build, use the 2.3 release.

1. Download

Download userChrome.css and userContent.css

2. Enable custom stylesheets

In Firefox, go to about:config and set:

toolkit.legacyUserProfileCustomizations.stylesheets = true

3. Find your profile folder

In Firefox, go to about:support and click Open Profile Folder.

4. Copy the files

Create a chrome folder inside your profile folder if it doesn’t exist, then copy these files into it:

• userChrome.css — browser UI styling
• userContent.css — new tab / home page colors

5. Restart Firefox

The theme applies on restart.

6. Color Theme

FoxOne now includes a built-in Gruvbox inspired Dark color theme that activates automatically in dark mode. No separate extension needed.