No gamesThis is a total guess but do you have any addons installed that would take up a lot of space? Specifically games?
Download and run CCleaner. They're temporary files that CCleaner will clear out.
Firefox sucks anyway. Chrome is much better. But CCleaner should fix this issue temporarily.
It's a matter of preference i'd say.Just as many dislike firefox that dislike chrome.Many can't stand both & IE too.I may give pale moon a try this week.I believe the files are gone for good.I use secure file deletion in ccleaner.Even ran advanced system care after I was done