I was having really bad time with the constant adblocker warning pop-up yesterday so I disabled all other extensions, restored uBlock Origin to the default settings aswell as cleared the catche and updated filter-lists. Then I cleared all Firefox cookies and restarted it. This morning I did not get the warning unlike the few past days, so far so good. I’m sure this isn’t a permanent fix, but for those of you still struggling with it, these are the steps you might want to try.