As a fellow Firefox user this is not my experience at all. Most stuff works fine once I allow the necessary subset in uMatrix. Some things are a pain in the ass, like embedded video widgets that need to load in dozens of scripts from all over the web before they'll finally get to the actual video frames, but I can pretty much always get stuff to work.

One tip: Don't try to install too many general filtering extensions (uMatrix, Privacy Badger, uBlock Origin, etc...) at the same time because they will end up fighting.