A thing that's super frustrating is how the existence of service workers means entire groups of websites (say, all Google service simultaneously) will suddenly stop working unless I go into the Firefox "Task Manager". This is a critical part of using a computer like cmd-opt-esc was in Mac OS 7 or ctrl-alt-del was in Windows 95, but it's not foregrounded as well as it was in those old OSes. The browser recreated a problem from 90s computing but didn't recreate the solutions from that era