Talking about updates: Your attached Troubleshooting Information shows that you posted with a Firefox 80.0 version and not a recent release (current is 118.0, released last Tuesday), so you are quit far behind on updates. Has your Ubuntu version reached end-of-live and receives no longer updates?

You can find the full installer of the current Firefox release (118.0) in all languages and all operating systems here:

• https://www.mozilla.org/en-US/firefox/all/#product-desktop-release
• https://www.mozilla.org/en-US/firefox/118.0/releasenotes/

Verify that you meet the System Requirements (GTK+ and GLib) for the current Firefox release.

• https://www.mozilla.org/en-US/firefox/118.0/system-requirements/

Switched to a system with Firefox 118.0 and there still does not seem to be any option to put the tab bar back where it belongs.

You can only achieve this via code in userChrome.css, so it is up to you whether to go that route.

You can look at this thread for CSS code in userChrome.css for Firefox 112+ to move the tabs to below the Navigation Toolbar.

• /questions/1410524 FF 112 Tabs on the bottom beneath the bookmarks toolbar

Other possible CSS code:

• https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/tabs_on_bottom.css

It is not that difficult to create userChrome.css if you have never used it.

The first step is to open the "Help -> Troubleshooting Information" page and find the button to access the profile folder with the random name (xxxxxxxx.default-release).

• https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox

You can find the button to go to the profile folder under the "Application Basics" section as "Profile Folder -> Open Folder". If you click this button then you open the profile folder in the Windows File Explorer. You need to create a folder with the name chrome in the profile folder with the random name (name is all lowercase). In the chrome folder you need to create a plain text file with the name userChrome.css (name is case sensitive). In this userChrome.css text file you paste the text posted. On Mac you can use the TextEdit utility to create the userChrome.css file as a plain text file.

In Windows saving the file is usually the only time things get more complicated because Windows can silently add a .txt file extension and you end up with a file named userChrome.css.txt. To avoid this you need to make sure to select "All files" in the dialog to save the file in the text editor using "Save File as".

You need to close (Quit/Exit) and restart Firefox when you create or modify the userChrome.css file.

More info about userChrome.css/userContent.css in case you are not familiar:

• https://www.userchrome.org/what-is-userchrome-css.html
• https://www.userchrome.org/how-create-userchrome-css.html
• https://www.userchrome.org/firefox-changes-userchrome-css.html

In Firefox 69 and later you need to set this pref to true on the about:config page to enable userChrome.css and userContent.css.

• about:config => toolkit.legacyUserProfileCustomizations.stylesheets = true
• https://support.mozilla.org/en-US/kb/about-config-editor-firefox