uBlock Origin is effective at blocking those fake updates from appearing, as reported by a number of users. And that worked for me when I compared results using two separate Profiles; one "test" Profile that is "as installed" without uBlock Origin or other customizations, and my regular Profile where I used uBlock Origin all the time. https://addons.mozilla.org/en-US/firefox/addon/ublock-origin/ As far as this problem with those fake update notices overall, this has been going on for like 5 weeks now. Mozilla is well aware of this situation and a number of support contributors here have been tracking what's happening in this thread - https://support.mozilla.org/en-US/forums/contributors/712056?last=69573 - which was started by James who is a Moderator on this fora. The fake update files have been submitted to AV scans and the AV companies should be aware of what's going on. But it seems that the purveyor of this malware is creating new domains daily to stay one step ahead of getting shutdown completely.