hi, this is not the default behaviour of firefox - please make sure that you don't use extensions that might interfere here...

Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

Tab Mix Plus was the problem. But solving that created another huge problem. TMP is an essential addon for me. It makes firefox much more flexible in terms of the tab bar and the tabs. Now, all my customizations are gone. Bummer.

thanks, please make sure that you have the most recent available version of TMP installed or if it's still exhibiting that bug, you could report that at http://tabmixplus.org/forum/viewforum.php?f=2 since the addon's developers are usually quite fast to fix things

TMP was updated 6/10, so I think that it's the latest ver. Thnx for the link