Firefox had a new update last week or so, and lots of users had issues with add-ons. I was this close to uninstalling just to get my adblock back
But I stuck it out and they fixed it.
Never had an issue with VPN during that time, that must have been for certain providers.
Sorry you're having an issue; if it were me, I'd just try several different browsers until you got the results you want.
That, or try to connect to a different node for a little while til Firefox gets another update out.
Cheers