Customisation

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.

Looking for the squared corners look on windows 11? This way!

Want FoxOne with genuine Windows 11 Mica transparency? Take a look at Wintego’s fork – Firefox-transparent-theme.

All configuration lives in the :root block at the top of userChrome.css.

Color Palette

Layout

Rounded corners

FoxOne is square by default. Set --uc-rounded: 1 if you want FoxOne’s layout with the corners the rest of Windows 11 (and stock Firefox) has:

--uc-rounded: 1;

Every surface FoxOne squares then takes --uc-border-radius (8px), and the rows inside those surfaces take half of it (4px). That is the same pair Firefox ships in its own design tokens, so the result reads like stock Firefox rather than like a theme with one radius painted over everything: arrow panels, context menus and their rows, the URL field and its breakout box, tabs, find bar, status panel and split-view footer.

Change the radius itself with --uc-border-radius; --uc-rounded only decides whether it is applied or zeroed.

The in-content pages (about:preferences, about:addons, about:logins and the rest of about:) are styled by userContent.css, which cannot read userChrome.css’s variables. Its CONFIG block carries the same two variables; set --uc-rounded: 1 there as well and the cards, rows, buttons, fields, dropdowns, message bars and the category nav on those pages follow. The pages use one radius (--uc-border-radius) for everything rather than the three stock Firefox runs there, so they share one shape language with the chrome.

What it deliberately does not touch:

• Layout. The content area and the frames around toolbox, sidebar and browser stay square. Firefox only rounds those because it insets them by 4px first; FoxOne is edge-to-edge, and rounding them without the inset cuts notches into the page and alongside the sidebar. That is a layout change, not a corner.
• The URL bar’s internals. Row hover, icon chips and result buttons stay square, and are invisible either way since FoxOne draws them without a background. Only the painted shell rounds.
• How popups are drawn. FoxOne draws its popups itself rather than using the Windows 11 Mica backdrop, which is what keeps the palette Gruvbox instead of system-tinted. That path also gives the corners proper antialiasing, so no radius here renders as a staircase.

Tabs

Window Controls

Visibility Toggles

The dynamic bookmarks bar is adapted from LittleFox (MIT).

Since 3.5 it is on by default. Set Firefox’ bookmarks toolbar to Always show (right-click the toolbar area → Bookmarks Toolbar → Always Show) and it hides itself until you reach for the URL bar, giving the line back to the page. Since 3.5.2 a fresh tab keeps the bar visible until you navigate, so a new tab lands you straight on your bookmarks. Set --uc-dynamic-bookmarks: 0 for the previous behaviour, a permanent row below the toolbar, or --uc-dynamic-bookmarks-newtab: 0 to keep fresh tabs hover-only.

Adaptive Tab Bar Colour

FoxOne is compatible with the Adaptive Tab Bar Colour extension out of the box, with no configuration needed. When the extension is active it retints the frame, toolbar, URL field, popups and sidebar to match each page, and FoxOne yields those surfaces to it, collapsing the extension’s separate tones onto one flat colour so the one-line bar stays seamless. FoxOne’s structural layout and its accent cues (selected-tab line and title, focus ring, container glow) stay in place, so the one-line look survives the recolour.

The hand-off keys off the lwtheme attribute Firefox sets on the root element whenever a theme extension is active: FoxOne sets no lightweight theme of its own, so with no such extension installed it keeps painting its own Gruvbox palette exactly as before. The same mechanism applies to any dynamic-theme extension that uses Firefox’s standard colour variables.

The selected tab’s title stays in the accent colour by design. On a near-white page colour that is lower contrast than the rest of the chrome; it is a deliberate identity trade-off, not a bug.

FoxOne’s hover and selection cues use accent-coloured text rather than background blocks, which reads best on dark surfaces. Under Adaptive Tab Bar Colour a light page colour can make them look off; for the best result pair FoxOne with dark mode and Dark Reader instead.

Scrollbar (userContent.css)

Find Bar