Comment by nateb2022

See https://bugzilla.mozilla.org/show_bug.cgi?id=1716164

My guess is that Firefox was being served AV1 by YouTube. Intel chips prior to 11th gen have no hardware decode support for AV1, and so your CPU was overworked and bottlenecking.

Chrome and Safari probably resorted to H.261/H.263/H.264 encoded video from YouTube, and relied on the hardware decoder.

Easy fix: go to `about:config` and disable `media.av1.enabled`.