Are you running McAfee? Show the issue by posting full screen screenshots and not just of the pop-up. It doesn't sound like a browser issue, but more of a process running and generating the pop-up. You sound infected!!!

I'm getting those same extremely annoying pop-ups supposedly from McAfee (because every time I click on one, an ad to sign up for McAfee comes up). They may be 3rd party ads but they are all for McAfee. I've uninstalled my previous McAfee program and ran a full scan on Windows Defender. It found to Trojans and scrubbed them both but when I logged into Firefox again, the same pop-ups (sometimes 3 at a time) started coming back up warning of viruses (which I know is bullshit!). I'm also a bit annoyed that I'm having to post about this on a "community board" because I can't find a direct contact to Mozilla Firefox. I've used Firefox for about 3 decades or more but if this crap keeps happening and Mozilla hasn't addressed it, I'm going to change browsers!

That McAfee popup is not from Mozilla nor the Firefox web browser nor is Firefox the cause of why you are getting it.

Spot fake McAfee notifications https://www.mcafee.com/support/s/article/000001899?language=en_US

There is or was a better McAfee article that had a image of that fake alert you posed a image of but they made it access denied for some reason.

This kb article is more for web push notifications that popup on the bottom right corner of Firefox windows from sites the user has allowed to send notifications however it may help still https://support.mozilla.org/en-US/kb/push-notifications-firefox

I'm also a bit annoyed that I'm having to post about this on a "community board" because I can't find a direct contact to Mozilla Firefox.

Mozilla Firefox is the name of the web browsers and not a company or such as that would be Mozilla.

All of the web browsers have a community support forum of some sort as none of them provide direct support whether by phone, chat or email especially since they are free to download and use. Except maybe for enterprise users who pay for it as Mozilla is now doing such a service starting in January 2026 https://support.mozilla.org/en-US/forums/support-forum-contributors/717449

Subscription based products can come with one on one support by phone, chat or email like with some antivirus clients and such because you paid for that as part of their subscription.

Mozilla does have a few subscription based products as in Mozilla VPN, MDN Plus, Firefox Relay Premium. Mozilla also had two more subscription products as in Pocket Premium that ended in July and Monitor Plus that ended as of Dec 17. In this case you can get direct ticket support as part of the subscription.