there are both configurable mice that let you swap mouse buttons (in the worst case in a windows virtualbox with usb passthrough) or mice that are leftie right out the get-go. those would allow you to use wayland, assuming you can afford to and want to get a new mouse.

with linux and kde you could create an encrypted kde vault that’s mounted to your librewolf profile folder (and you can change librewolf settings to save history, cache, etc.)

if you don’t want to use kde, it uses cryfs in the background, which has a cli tool as well. unmount the volume after using the browser and profit i guess, though i do agree with the other commenter that this doesn’t make much sense in my head.