Created attachment 136203 [details]
Task panel

SUMMARY

The pop-up in the task manager shows the correct picture of the task window for Firefox until you start playing video (in my case of Youtube)


STEPS TO REPRODUCE
1. Go to the Task Manager Settings -> Behaviour
2. Change Group: to "do not group", and save
3. Open Firefox with, for example, this site.
4. Open a new window of the Firefox with some other side.
5. When you place your mouse over each task in the Task Panel, you'll see the correct picture for each Firefox window
6. Open a new Tab in any Firefox window, go to youtube and start any video. Pause it.

OBSERVED RESULT

Now the both Task manager's panel buttons show the same picture of the youtube window even if you change the active tab of the window with youtoube.

EXPECTED RESULT

Each Task Manager panel button must show the actual window for current tab for each Firefox window


SOFTWARE/OS VERSIONS
Operating System: Slackware-current
KDE Plasma Version: 5.21.1
KDE Frameworks Version: 5.79.0
Qt Version: 5.15.2
Kernel Version: 5.10.18
OS Type: 64-bit
Graphics Platform: X11
Processors: 12 × Intel® Core™ i7-9750H CPU @ 2.60GHz
Memory: 31.1 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics 630