Additionally, when I click on the " + " sign at the top of the browser, to open a new Tab, a new WINDOW opens, a tab cannot be opened. BUT, in that New Window, click on the plus sign, and it works properly. A tab opens.

This has, of course, destroyed all the open tabs I had, and thus my current areas of interest and browsing history.

Once again, I should like to suggest that the equivalent of the "Restore Point" in windows operating systems be provided for the browser.

My only wild guess is to make sure -- browser.tabs.tabmanager.enabled -- is True. Copied it to make arrows for Tab Overflow but it seems logical to chk it. I made/keep a Test Profile to Test such things and have find Troubleshoot Mode (FF Safe Mode) doesn't always behave the same as a Test Profile.

Thank you. I checked that several times, during which checks it did not work.

BUT, I have now checked again, it now does work. Weird.

Thank you for the prompt

A S Beesley