alt Hacker NewsI don't think youtube playback is a relevant comparison since it uses ~0 CPU. Pretty much all phones have hardware accelerated decoding. Lots of TVs and streaming devices use an ancient Android phone SoC yet they too can play YT and run a browser. The entire UI is often a local web app.
I imagine, be he mentions video playback on youtube making things worse, and he does have a dedicated amd gpu.
But iirc for both Firefox and chromium on Linux desktop hw acceleration is tricky so maybe it's that.