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.

Right-click an empty spot on the toolbar and pick Bookmarks Toolbar → Always Show.

Sounds backwards for a one-line theme, but that is what hands the bar to FoxOne: since 3.5 it no longer sits on a row of its own. It hangs below the toolbar, out of sight, and fades in when you reach for the URL bar — move the pointer down onto it and it stays open until you leave. The page keeps the line. Since 3.5.2 a fresh tab shows the bar outright, no hover needed, until you navigate somewhere.

Leave the setting alone and nothing changes; Firefox keeps the bar collapsed and there is nothing to reveal. If you would rather have the classic permanent row, set --uc-dynamic-bookmarks: 0 in userChrome.css — see Customisation.