I had the same problem yesterday, restarting Firefox helped for a bit, but then it recurred. I'm not entirely sure what's happening--I'm assuming it's not Firefox itself, as I hadn't updated it (even if there was an update). I kind of assumed it was an extension proble as I noticed on YouTube first (so I assumed it was them changing something to block add blockers), but it was universal to other websites as well. No idea.
I had the same problem yesterday, restarting Firefox helped for a bit, but then it recurred. I'm not entirely sure what's happening--I'm assuming it's not Firefox itself, as I hadn't updated it (even if there was an update). I kind of assumed it was an extension proble as I noticed on YouTube first (so I assumed it was them changing something to block add blockers), but it was universal to other websites as well. No idea.