Firefox 82.02
Plasma Browser Integration 1.7.6
Plasma 5.20.2
Since this last update, every time a video stops playing in my desktop browser (even those obnoxious ones that play automatically as you scroll), a media control notification is popping up on my phone, which in turn pops up a notification on my desktop.
Although this isn’t really causing any functional issues, it is highly annoying behavior.
I’ve been experiencing the same and it made me turn off the plugin that handles media controls on my desktop. Downside is that I can no longer control media on my pc from my phone.
Same here with chromium.
Same here. Turned off multimedia controls on my phone. Problem gone. But no solution I guess 
You should disable in your phone notifications from KDE Connect. Go to Plugin settings > Notification sync and uncheck KDE Connect. You can also disable phone notifications for media control (this option also disable desktop notifications) in Multimedia controls
