I was just about to give up on Firefox when I discovered it was this add-on that basically maxed my CPU usage and rendered browsing impossible, let alone multi-tasking.

works like a charm; love the schedule function

コントラストも設定されていて使いやすいです。

slow down Firefox. Can't change per website, only global.

Works like a charm and the dark theme is of the right contrast

My eyes are saved.
I would like to have a "dark-ish" mode so as to not have white on black (which also strains my eyes), but I manage with just making everything sorta greyscale and increasing the sepia value.
Would recommend.

Works really well for most sites, but I'd love to be able to tweak specific websites in finer detail than picking which dark mode style and color choices. Namely, making Google Docs/Sheets/etc UI grey and black but keeping the document content itself intact. It's annoying having to overwrite code in the dev tools every time I want to use Docs and preserve colors when formatting is very important (since those changes are wiped out once you close Firefox).

Dark theme detection also usually works but can be spotty.