How to Disable Firefox's Nova Redesign on Linux

Firefox 157 lands at the end of September, and with it comes Nova, the pastel-tinted, rounded-corner redesign Mozilla has been quietly refining since March. If you run a carefully tuned GTK or KDE desktop and you've spent years making Firefox's chrome match your system theme, Nova is about to undo that work for you automatically. The good news: you can turn it off, at least for now.

Nova brings floating toolbars, softened corners, gaps that segment the interface into visual blocks, and web content that no longer sits flush against the window edges. Mozilla dialed back some of the more aggressive gradient work after early feedback, but the core shift is still a departure from Firefox's traditional flat, dense chrome. For Linux users running GTK themes like Adwaita, Yaru, or a custom Kvantum setup on KDE, this matters more than it does elsewhere. Firefox has historically done a reasonable job blending into GTK and Qt environments, and Nova's new floating elements and rounded frames don't always respect the theme engine the way the old UI did. Expect visible seams where Firefox's own styling fights your system theme, particularly around window decorations and toolbar backgrounds.

Flipping the about:config switches

The fastest way to opt out is through Firefox's hidden configuration page. Type about:config into the address bar, accept the warning, and search for browser.theme.nova. Set it to false. On builds where Mozilla has split the feature into smaller flags, you'll also want to check for browser.proton.appmenu.enabled, browser.proton.toolbar.enabled, or similarly named toggles depending on which Firefox 157 build you're on; naming has shifted during development, so search "proton" and "nova" together to catch anything relevant. Restart the browser after any change, since theme flags rarely apply live. This pairs well with shotcut vs kdenlive: best free linux video editor? explained.

If Nova has already fully replaced the old rendering path in your build, flipping the flag might only partially revert things. Some users are reporting that toolbar rounding and spacing snap back to the classic look, but the new floating tab bar behavior sticks around. That's expected. Mozilla built Nova to eventually become the only option, and about:config flags are a temporary courtesy, not a permanent escape hatch. Treat them as a bridge, not a destination.

Worth noting: these preferences aren't guaranteed to survive future point releases. Mozilla has pulled deprecated about:config toggles before once a redesign matures past its rollout phase. If you're building a workflow around disabling Nova, don't assume browser.theme.nova will still exist in Firefox 160.

userChrome.css and the GTK theme problem

For anyone who wants finer control, or who finds the about:config flag insufficient, userChrome.css remains your best tool. If you haven't used it before, you'll need to enable it first: go to about:config, set toolkit.legacyUserProfileCustomizations.stylesheets to true, then create a chrome folder inside your Firefox profile directory (usually ~/.mozilla/firefox/yourprofile.default/chrome/) and add a userChrome.css file inside it.

From there, you can target Nova's new CSS classes directly. Nova introduces new selectors for the floating toolbar container and the rounded tab elements, so rules like #TabsToolbar, #nav-bar, and the newer .toolbar-items wrappers are where you'll spend your time. Setting border-radius to 0 across these elements strips the rounding. Removing margin and padding values that Nova adds around the toolbar container restores the old flush-to-edge look. This takes some trial and error since Mozilla hasn't published a stable style guide for Nova's internals, and class names can shift between beta and stable channels.

Here's where Linux users specifically hit friction that Windows and Mac users don't: GTK theme integration. Firefox on Linux uses GTK's native widget rendering for certain UI pieces, like scrollbars and some dialog chrome, while using its own CSS for the rest. Nova widens that gap. You'll likely see mismatched corner radii between Firefox's Nova-styled toolbar and your GTK theme's window decorations, especially on GNOME with Adwaita or Yaru, or on KDE with Breeze combined with a GTK compatibility layer. If you use a GTK3 theme that already applies rounded corners to headerbars, Nova's own rounding can double up and look worse than either default. The fix is usually to zero out Nova's border-radius values via userChrome.css and let your system theme handle the rounding alone, rather than fighting both layers simultaneously.

Users running window managers without traditional title bars, like i3, Sway, or a tiling setup under GNOME, face a different issue. Nova's floating toolbar design assumes some breathing room around the browser window that a title bar normally provides. Without one, the floating elements can look oddly disconnected from the rest of the interface. Adding a small negative margin to the toolbar container in userChrome.css tends to close that gap, though the exact value depends on your window manager's gap settings.

One more practical note: extensions that already modify Firefox's chrome, like various GNOME Shell integration add-ons or theme-syncing tools, may conflict with Nova's new DOM structure. If your toolbar looks broken after updating to 157, disable third-party chrome-modifying extensions first before troubleshooting userChrome.css, since that's the more common culprit.

None of this is a permanent solution, and that's the point worth sitting with. Mozilla has made clear that Nova is the direction Firefox is heading, and about:config flags plus userChrome.css hacks are stopgaps for people who aren't ready to switch yet, not a long-term alternative to the new design. If you're deeply invested in matching Firefox's chrome to your GTK or Qt theme, this is a good moment to decide whether you want to keep fighting that battle release after release, or start planning for a Firefox that looks less like your desktop and more like Mozilla's own vision of it. Either way, back up your userChrome.css tweaks now, because you'll likely need to revisit them with every Firefox update until Nova fully settles.