How to switch back to Firefox' old style of tabs?

The recent update (89 I think) causes all tabs to render in the same continuous shading, which makes it somehow more difficult to spot each tab's start and end (regardless of the favicon, I'm sorry, silly old proper borders just were easier on my eyes). How do I get that back? I tried this related answer's browser.proton.enabled=false to no avail, and re-enabling compact mode also did only partially restore the previous look and feel. How can I get good old tab shading and borders back?

Solution 1:

In Firefox 91, restore the old tab style as follows:

1. Open about:config.

2. Search for toolkit.legacyUserProfileCustomizations.stylesheets.

3. Double-click the value to set it to true.

4. Open about:support.

5. Search for Profile Directory (or Profile Folder).

6. Click Open Directory (or Open Folder).

7. Create a directory named chrome.

8. Navigate into the chrome directory.

9. Create a new file inside chrome named userChrome.css.

10. Copy and paste the following code into userChrome.css:

     .tab-background {
       border-radius: 0px 0px !important;
       margin-bottom: 0px !important;
     }
    
     .tabbrowser-tab:not([selected=true]):not([multiselected=true]) .tab-background {
       background-color: color-mix(in srgb, currentColor 5%, transparent);
     }
    
     menupopup>menu,
     menupopup>menuitem {
       padding-block: 2px !important;
     }
    
     :root {
       --arrowpanel-menuitem-padding: 2px !important;
     }
    

11. Save the file.

12. Restart Firefox.

The old tab style is restored.

Solution 2:

Not surprisingly I'm not the only one disliking this, and fortunately there's already a fix called Lepton at https://github.com/black7375/Firefox-UI-Fix#installation-guide. It still doesn't feel 100% proper, but so much better already with simple tab separators.