I don't know for you, for me this is huge.

New versions of Firefox removed some support for extensions that allowed multiple tab rows.

Here is how you can enable it:

1. Type about:support in url field of firefox, hit enter.
2. On the ‘Profile Folder’ setting (about 8th from the top) click the ‘Open Folder’ button.
3. Create a ‘chrome’ subfolder, if you don’t already have one.
4. Inside that folder create a file called ‘userChrome.css’ (right click > new > text document – make sure to name the file userChrome.css and not userChrome.css.txt or something)

5. Firefox 65 and newer:
Open the file for editing and paste the contents of this file: https://github.com/MrOtherGuy/firefo...i-row_tabs.css
Versions before Firefox 65:
Open the file for editing and paste the contents of this file:
https://gist.githubusercontent.com/f.../gistfile1.txt
6. Restart FF and you should have multi row tabs

Thank you for your help!