edge-frfox repaints Firefox to look like Microsoft Edge

It is a CSS file that overrides the browser chrome

Edge-Frfox is a Firefox userChrome.css theme that aims to recreate the look and feel of Microsoft Edge, and the mechanism is the standard one for that kind of project. The repository has a chrome/ directory holding the stylesheets, a user.js file, a sidebery.json configuration and a screenshots/ directory. Installing it means putting the chrome folder and the user.js file into your Firefox profile directory, which you open from about:support with the Open Folder or Show in Finder button for the root directory of your browser profile. Then you close and restart Firefox, and if it was done correctly the theme is installed. That is the whole installation. There is no extension to approve, no package to build and no setting to enable, which is why a theme of this kind is a five minute job and why it can equally be undone in five minutes by removing the two items again.

Every optional behaviour is a boolean preference

The design decision that makes this theme more than a stylesheet is the tweak system. Certain tweaks can be applied to the theme, and to enable them you navigate to about:config and create a boolean key for each tweak you want to use and set it to true. To disable a tweak you set the key to false or delete it. The keys are namespaced under uc.tweak, so uc.tweak.floating-tabs emulates the rounded tabs feature available in Edge, uc.tweak.rounded-corners adds padding and rounded corners around the browser window, uc.tweak.hide-tabs-bar hides the tabs toolbar when using a vertical tabs extension, and uc.tweak.theme.sidebery enables the Sidebery extension sidebar theme. The effect is that the theme ships as one CSS bundle and the features are selected at runtime by the preferences, so you are not maintaining a fork of the stylesheet to turn a feature off.

The tweak list covers the Edge details people actually notice

The list is long enough to show what the theme is trying to match. Beyond floating tabs, rounded corners and the hidden tabs bar, there is a variant of the hide tabs bar tweak, uc.tweak.hide-tabs-bar.no-window-controls, which additionally hides the window controls from the navigation bar. There is uc.tweak.disable-drag-space, which removes the additional space at the top of the window above the tabs that appears when the window is not maximised, so the tabs touch the top edge at all times. There is uc.tweak.newtab-background, which adds a custom background image to the new tab page, where you put an image named background-0.(jpg/png) in your chrome folder and optionally a second one named background-1.(jpg/png) that is selected when the dark theme is enabled. There is uc.tweak.hide-forward-button, which hides the forward button when it is not needed, as seen in Edge, and uc.tweak.hide-newtab-logo, which hides the Firefox logo and wordmark on the new tab page. Two more are about small behaviours: uc.tweak.force-tab-colour, which removes the ability for custom themes to change the colour of selected tabs so they match the toolbar colour, useful with themes designed for the default Proton style, and uc.tweak.vertical-context-navigation, which displays the navigation buttons in the right-click menu vertically like the other menu items.

The Sidebery integration is the deepest part of the theme

The Sidebery section is the one that goes beyond skinning, because it is a theme for another extension's sidebar. You download and install Sidebery from the Firefox addons store, and the theme enables a matching colour scheme for it, usable with or without the hidden tabs toolbar tweak. The readme flags that on Linux the colour theme may not work properly, and the fix is to enable the auto: dark/light colour scheme option inside Sidebery, with the trade-off stated plainly: that disables the custom Firefox theme colours and uses the system light or dark colours instead. The readme also lists recommended Sidebery settings in a collapsible block, covering the context menu, the navigation bar layout, what to show in the bottom bar of the tabs panel, new tab button behaviour and position, pinned tab position and titles, and the appearance section where the theme is set to proton with the colour scheme as firefox. Alternatively you can import the provided sidebery.json configuration file, with the caveat that this restores Sidebery to the default settings before applying it, and the readme says the tweak key uc.tweak.theme.sidebery turns the theme on.

A few about:config preferences complete the Edge look

Four browser preferences sit alongside the theme's own tweaks, and they are the ones that change how the window behaves rather than how it is painted. The macOS native context menu is replaced by the Edge themed one with widget.macos.native-context-menus set to false. Light theme in private browsing mode is set with browser.theme.dark-private-windows set to false. Rounded bottom window corners on Linux are enabled with widget.gtk.rounded-bottom-corners.enabled set to true. And the Windows accent colour in the tabs toolbar is enabled with browser.theme.windows.accent-color-in-tabs.enabled set to true, which requires the Windows show accent colour in title bar option to be on. The readme notes that the theme is most frequently tested on macOS, and the screenshot given as the reference is macOS with Firefox 120, with rounded corners and the hidden forward button enabled.

What this theme is not

The obvious boundary is that it is a userChrome.css theme, so it only affects the browser's own interface and not the pages you visit, and it only works in Firefox. The second boundary is the one that matters more, which is that a userChrome.css reaches into internal Firefox chrome, and internal chrome is not a stable interface. When Firefox changes the markup or the CSS custom properties the theme relies on, the result is usually a partially broken interface rather than an error, and the theme's own release history shows how far back its own support goes. The newest tagged release is v24.4.18 from April 2024, with v24.4.10 from a week earlier and v24.2.19 from February 2024, while the last push was on 2026-09-29, so the working tree is being maintained without a matching release. The screenshots table is a useful check on what to expect, with entries for the default Windows 11 look, floating tabs plus rounded corners, the hidden tabs bar with rounded corners and a Sidebery theme on macOS, and a Linux entry using the Ubuntu Yaru theme, each in light and dark.

Editorial conclusion

edge-frfox suits a Firefox user who wants the Edge layout, particularly the floating or rounded tabs, without giving up the browser, and it suits anyone who prefers toggling features through about:config over maintaining a patched CSS file. It is the wrong tool for someone on Chrome or Safari, since it is a Firefox userChrome.css theme, and it is the wrong tool if you want a fully supported interface, because a userChrome.css overrides internal Firefox chrome and will break when Firefox changes. Before installing, read the note that the theme is most frequently tested on macOS, and check the Firefox 120 screenshot, since the layout depends on the browser version. The last push was on 2026-09-29 and the newest tagged release is v24.4.18 from 2024-04-18.

Frequently asked questions

Official sources

1. bmFtZQ/edge-frfox on GitHub
2. Issues
3. License: MIT
4. README
5. Releases