When you let Firefox open for long on work on it a lot, some domains stop to load, it means for example that for a period your youtube website will work normally, but after a while if you try to open anything from youtube it will load a black page and nothing else, you can refresh or try whatever you want, all the "youtube domain" is blacklisted until you kill Firefox and reopen it freshly It happens to me since forever, on all OS, on many different devices, I learned to live with it, but I was bored and I was obliged to work on other browsers for a while where you don't experience things like that and at your return in Firefox it becomes big so I ended up posting it here It's maybe related to cache (not the cache that you flush with ctrl-F5, this isn't working but), a sort of cache related to Firefox process, the Web handler/content module maybe, I don't know. I guess that if maybe you can clean from the actual process all the data concerning the domain, it will load nicely without reloading all Firefox The step to reproduce are quite difficult as you see here but i'm sure that i'm not the only one experiencing that