I don't mean half the websites don't work. I mean half the time Firefox won't load ANYTHING. It basically stops working with any DNS for a few hours at a time.
I have had this issue a few times and find that usually there is some weird update or something behind the scenes and a reboot of Firefox lets it start loading again. I'm not techy enough to know why but I have found that closing all tabs is mandatory maintenance for Firefox every so often.