A custom userChrome.css for Firefox 86+ (Beta, Developer and Nightly for February 2021). For personal purpose only.

(Firefox Browser Proton Custom - Firefox Browser 86 Developer Edition - elementary OS Dark Theme)

(Firefox Browser Proton Custom - Firefox Browser 86 Developer Edition - elementary OS DefaultTheme)

(Firefox Browser Proton Custom - Firefox Browser 86 Developer Edition - Windows 10 Dark Theme)

(Firefox Browser Proton Custom - Firefox Browser 86 Developer Edition - Windows 10 Default Theme)

• Your must enable via about:config the toolkit.legacyUserProfileCustomizations.stylesheets, browser.proton.enabled and browser.proton.tabs.enabled in Firefox.

• Download the userChrome.css file (for Firefox Browser 86+ version) and save it (right-click -> Save Link As...) to your Roaming\Mozilla\Firefox\Profiles\[User]\chrome folder (%APPDATA%\Mozilla\Firefox\Profiles\ on Windows) or go to about:profiles (in Firefox) and locate the Roaming folder of your profile.

• Restart Firefox to see the changes.

Firefox-Browser-Proton-Custom is a more "cleaner" version of my custom Firefox-Browser-UI-Custom and aditionally has some extra things like:

• Revert to some Firefox standard items, but keeping the customized url-bar, close button hovering over unselectd tabs, widgtets panel and useful go-arrow button.

(Firefox Browser Proton Custom - Firefox Browser 86 Developer Edition - elementary OS Dark Theme)

(Firefox Browser Proton Custom - Firefox Browser 86 Developer Edition - elementary OS Default Theme

(Firefox Browser Proton Custom - Firefox Browser 86 Developer Edition - Windows 10 Dark Theme)

(Firefox Browser Proton Custom - Firefox Browser 86 Developer Edition - Windows 10 Default Theme)

This userChrome.css file use code snippets collected from other sources, so the credits (mostly) are for their authors:

• https://github.com/axydavid/FirefoxUI
• https://github.com/gabeweb/Firefox-Quantum-UI-Lite
• https://github.com/muckSponge/MaterialFox
• https://github.com/coekuss/quietfox
• https://github.com/Timvde/UserChrome-Tweaks
• https://www.reddit.com/r/FirefoxCSS/

Yes, the theme is a fork of forks of other projects, so there are many bugs in the code, for example the context menus do not properly reflect the shadows in all environments, nor does the background color of the side panel context menus change (Firefox Browser Nightly 78 "breaks" some things).

I'm not a programmer, but at least I tried to make a new theme for al Firefox users 🤘🏻

Suggestions and ideas are very, very welcome!