Firefox Proton UI fix

Restores the classic tab style (Firefox 89 or newer)

The new Proton UI appeared in Firefox 89 and I'm one of those people who want back the classic tabs.

Motivation

Setting the browser.proton.enabled option to false is not working anymore since Firefox version 91. I love Firefox, but I was really upset to see there is no option anymore to turn back on the classic style. I decided to do some research in order to find an option to alter the user interface, and 15 minutes later this project was born. It is as it is, just a quick fix :)

Installation

1. Enable legacy CSS

Start Firefox, and navigate to about:config
Set toolkit.legacyUserProfileCustomizations.stylesheets to true

2. Find out where is your profile data stored on the disk

Still in Firefox, navigate to about:support
Find the row starting with Profile Folder, and click the Open Folder button.
After you clicked the button, your profile folder is opened in the Windows File Explorer.

The profile folder path is something like this:
C:\Users\YourUsername\AppData\Roaming\Mozilla\Firefox\Profiles\abcd123.default-release

3. Create the "chrome" folder

Create a new folder inside your profile folder named chrome, then open it.

Your chrome folder should be located inside the profile folder like this:
C:\Users\YourUsername\AppData\Roaming\Mozilla\Firefox\Profiles\abcd123.default-release\chrome

4. Copy the CSS file

Download the chrome/userChrome.css file from this repository.

Copy userChrome.css into your chrome folder.

C:\Users\YourUsername\AppData\Roaming\Mozilla\Firefox\Profiles\abcd123.default-release\chrome\userChrome.css

5. Restart Firefox

Restart Firefox to apply the CSS fix.

Dark theme

Dark theme fix available, just copy the CSS files from the chrome-dark folder.