A feature I slept on for way too long are adding custom search engines and assigning shortcuts to search engines for sites I use frequently. Some Firefox support articles explaining: add a search engine from the address bar and how to assign shortcuts to search engines. A ton of sites have search engines so it's really easy to set up.

For the Oldschool Runescape wiki I have an rs keyword so I can just hit Ctrl+l (hotkey that focuses the address bar) then search for something like "rs rune scimitar" and it'll take me straight to the wiki page for it. I'm also using it for Google Maps, Youtube, MDN, and NPM and have 1-3 character keywords for each, though those all go to a search results page it still saves me some time!