Avast web security keeps giving pop-ups on JS:Obfuscated-GP

[Avalin]

I got a pop-up about an infected website, and restarted Firefox after that. History and cookies and so on have been deleted, but I haven't reinstalled Firefox (yet).

Now I keep getting that same pop-up whenever I use Firefox. I have not been to the same website again; the pop-up last occured when I was still on google.com. Doesn't seem to happen in Chrome, or at least hasn't happened yet. Avast boot scan (set to search everything for anything and with highest sensitivity) finds nothing malicious, corrupt or other, nor does Malwarebytes.

Pop-up says the following every time:
Name of threat: JS:Obfuscated-GP [TrJ]
Type of threat: Trojan
URL: https://fmovies.to/film/carry-on-camping.52n2v
Process: C:\Program Files\Mozilla Firefox\firefox.exe
Found by: Web protection
Status: Connection aborted
5710457ac08c/211003.1412+0200

Please advice on how I get rid of this.

[Asyn]

-> https://forum.avast.com/index.php?board=4.0  (Best you post/ask in the dedicated forum section.)