i recently find that firefox is using far more system resources while playing videos from youtube as it was due to a bug in firefox that it can’t use Hardware Accelerated Video Decoding in wayland hence this high cpu usage.
now technically there is two solution ether switch to xorg(x11) or see below
1. Navigate to "about:config". 2. In the field at top where it says "Search preference name", type "gfx.webrender.all". 3. In the row where "gfx.webrender.all" appears, there will be a button on the right-hand side with two arrows. Click that button and confirm that the text in the middle of the row now reads "true". 4. Restart your browser.
if it causes any issues it can be revert back as normal