You can either try to start Firefox in safe mode by holding down the shift key while starting Firefox, which then disables all add-ons, to see if it’s an add-on causing the issue.
Or you can reset Firefox, which will give it a new default user profile with no add-ons added yet. Again, you can choose either of these options by holding the shift key, when you start Firefox and you’ll get a pop up box asking which you want to do.
OR, you could completely uninstall Firefox.
Then search for and remove any mozilla files/folders
Then download and reinstall fresh firefox. Make sure not to import anything from IE (except maybe your favorites).
See if that works.
K, did the shift key thing and still won’t go to YouTube, get that block error as unsafe ...
Well I totally removed FF and reinstalled it ... still the same thing, can’t get to FB or Youtube ... don’t know about other sites yet ...
And now FF won’t let you add on anything from their pull down menu ... says it’s an untrusted site. I hate IE and don’t want to use that ...