I use tridactyl in firefox. Except for emacs and tiling wms I’m not too deep in applications for reducing mouse usage, I tend to use keyboards with ‘better mouse placement’ for example the tex shura which copies the thinkpad trackpoint, or a corne keyboard with a pimoroni trackball. Or a charybdis nano. Even using a smaller keyboard layout counts imo, my favourite non-ergo keyboard layout is 60% which reduces necessary arm-travel-distance a lot :)