A media player has seized control of my computer!

It started when I moused over the Firefox icon on the task bar. All of the thumbnails were identical. I soon realized that they were always of the last YouTube video I watched. I rebooted, thinking that there was some KDE/Plasma glitch, but I then got somewhat inconsistent behavior: sometimes, the thumbnails represented the Firefox windows, and sometimes they were all of the last YouTube video I watched, but the captions to the thumbnails were always the title of the video. Lately, all of the thumbnails are always of the video—or of the last ad that played. The taskbar thumbnails have now been rendered useless for Firefox.

Then I noticed a video icon on the login screen. Clicking it plays the audio of the last YouTube video I watched! I certainly do not want active software hanging out of my login screen!

And now, whatever has taken over my computer has taken a recent irritating YouTube habit a step further. Lately, when you back out of a video on a playlist, YouTube “helpfully” pops the video out into a little box where I can keep watching it. What makes YouTube think that pressing the ‘Back’ button means I want to watch the video??? But I digress.

In the past day or so, when I press the back button through my history, I hear audio playing, even though I’m on the YouTube subscription page, and no video is playing. The Firefox icon on the taskbar indicated that a video was playing, but I could not find any sign of any active video on Firefox. Then I noticed some kind of video icon on the task bar that I did not put there. It is called “Media Player,” and it has taken on the task of playing videos and ads that I do not want to watch. Does anyone know what is this, where it came from, and how do I get rid of it?

Hi CousinRicky,

This sounds really weird. Is that “Media Player” any of those:
If yes, try removing it in “about:addons”.

I see no such add-on.

And now, my computer is getting hot and slowing down. I wonder if this PUP is causing that.

You might try starting firefox with an empty profile. First of all stop firefox and kill all lingering “child” processes. You can use KSysGuard to show the processes as a tree. (BTW, this can be used of course to see what process is putting so much load to your computer.)
Rename the related folder of the current profile or move it to some safe place. You will find the setting in “about:profiles”. Usually it’s something like “~/.mozilla/firefox/***.default”. If that works and you need data like bookmarks or your history you can copy the relevant files from the old profile to the new one. You’ll find the details here:https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data