As a university student, I found it frustrating to speed up my recorded lectures beyond 2 times. On a random night, getting sick of hearing a 3hr lecture, I searched for Firefox addons. I never thought I would find the exact solution to my problems.
I am now finally able to watch lectures at the speed my mind actually works at (and skip boring sections where nothing of value is said without potentially missing actually useful information).
Haven't found any issues yet while using it. Definitely works on Canvas if that's what you're worried about.