KDE: Application audio volume constantly drops to some value

Fedora 35, KDE Plasma.

I have Firefox browser opened. YouTube videos are opened in several tabs.

I open Audio Volume control. Devices / Speakers = 80%, Devices / Headphones = 80% (tried both). Applications / Firefox = 100% for all tabs.

Then I start playing video in a browser tab. Once it starts, the sound volume is automatically dropped: Applications / Firefox = 77%. While the video is playing I manually return the volume to 100%. Then after some time I pause the video. Then on resuming it the volume is immediately dropped: Applications / Firefox = 77%.

This occurs on every video start / resume. What can be a reason? How to stop this? Thank you.

A-ha-ha. I found the reason: the audio control reflects the volume set directly in the video object inside the web page. It can be adjusted in audio control, but this does not change the volume inside the web page. Pretty non-obvious, but solved.