Thunderbird has started appearing on all desktop activities
 

This never happened before: I restarted Thunderbird while displaying my KDE "Mail" activity and T-bird now appears on all activities as though I'd right-clicked on the title bar and select appear in all.

Trouble is, T-bird had no title bar any more so there's no place to right-click. (Thanks, Mozilla. Thanks a lot.)

Question: How to I restrict it to just a single activity to avoid cluttering up the other activities?

TIA...

UPDATE: I found that I had a strange T-bird process hanging around that wasn't displaying on the desktop. Issuing "pkill -9 thunderbird" appears to have corrected it AND allowed me to right-click on the taskbar to access the "Show in activities" menu. By default, T-bird appears to want to display everywhere. Weird.