I’ve been using Vimium for about a year now and really like it. I use it almost exclusively for fast keyboard-based scrolling, because I hate having to continuously rub my finger against a cold aluminium surface or spin a little plastic wheel to obliteration (maybe I’m weird). I know, arrow keys are a thing, but somehow I feel more at home with Vim keybindings.
Vimium has a lot of other great functions, but I don’t use them often enough to remember them, maybe I should.
However, I have to exclude it for a lot of webapps and websites where keybindings are used to trigger different events, which is sometimes annoying if you don’t know or forget about it.