Environment: OpenSUSE, KDE. Everything patched as of this morning.

My normal setup has multiple KDE activities with several of them running separate Firefox windows (with, of course, multiple tabs). On occasion, I'll minimize a Firefox window and it'll leave behind a "ghost" of the window on the desktop---a semi-transparent copy of the windows that I just minimized. Nothing, and I mean nothing (so far) short of logging out of the desktop and logging back in again will remove that ghost window. (Nothing disruptive about having to do that, you know.) When I log back in, and Firefox restarts, all of the windows pop up in a single activity which I then have to laborious;y move to the correct activities using the right-click menu on the window title and specify the target window with the "Show in Activities" menu. (It used to be possible to drag the icons in the Activity Manager to the proper activity but that broke months ago and hasn't worked lately. Different issue, though.) If, before moving the Firefox windows to the correct activity, Firefox decides to create one of these ghost windows, it will not follow the window to the activity I've relocated the browser window to---it continues to haunt the activity where Firefox was launched.

My wild guessing that this might have something to do with certain web pages but I've never been able to narrow it down to a single page. (At one time it appeared to be something related to visiting a page on forbes.com, now it seems to be something on discogs.com.)

What I haven't yet tried: Switching to a virtual console and then back to Xorg. I'll see if I can get a visit to Discogs to reproduce the problem and report back. (Even if that works, the question is: what's going on to require having to do that?)

Has anyone else seen this occur? If so, did you ever find a sure-fire fix for it?

TIA...

Have you ever logged out of Plasma and cleared the content from ~/.cache/? It's not unusual that the process stops inexplicable Plasma misbehavior.