Optimize Video Playback in Firefox on Linux

In between re-installing Arch on my Thinkpad T14s, I noticed some issues when using Firefox to watch videos on YouTube: After just a few minutes, my fans would spin up to an extent that quickly became very annoying.

Upon researching a solution, I came across RapidFox, which is a guide that explains some helpful parameters for Firefox tweaking. There, I found dom.media.webcodecs.h265.enabled, which was set to false. Turning it on enables hardware-accelerated H.265 decoding which seems to result in a much lower CPU usage, helping to keep the fans quiet.