Firefox has excessive GPU usage watching video.
Hardware acceleration is turned off. Firefox does not show the GPU usage in task manager (which is very worrisome in its own right) but when watching a single stream twitch.tv my GPU usage is 60%~100% (which only shows on the GPU tab of task manage). If I close firefox, the usage returns to 0%. The usage also becomes 0% when the stream is not the active tab.
I believe this is a recent behavior change as I noticed it due to it causing games to have low FPS. The excessive usage is also present with only firefox running.
This is happening on a 7800x3d, RX 7900 XT and 32GB of ram.
I also tested on youtube and found it to be using 10% less gpu on average but after while it settles down to ~30% usage.
If I enable hardware acceleration, Firefox uses the iGPU at ~50% usage and still uses 50%~60% of the dGPU. Performance of videos doesn't seem to change whether hardware acceleration is on or off (where as on chrome there is a very noticeable difference).
Used Chrome for sanity checks and it does not affect games FPS while using on average half the GPU usage of Firefox. Chrome also reports it usage in task manager correctly.
I suspect Firefox may be calling GPU encoder\decode hardware incorrectly and always using hardware encoders\decoders regardless of the hardware acceleration setting.