User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:72.0) Gecko/20100101 Firefox/72.0

Steps to reproduce:

The first time I've proceed with a reboot. The second time it corrupt Firefox and I need to reinstall my browser.

Paul, do you know if we can dupe this?

(To be clear, this is a spam/malware site that's spamming you and you should try to close it, if possible)

We've seen this kind of phishing page before, but from the screenshot I can't really tell what it's doing in this case.
Similar pages with this prompt tried to convince the user to install a malicious addons. They do this in fullscreen so they user does not click away. We've fixed this in Bug 1412561.
Perhaps there is also a prompt spam attack with the insecure form warning (bottom prompt), but so far I wasn't able to reproduce that.

We can probably make this bug public, I'll leave that to Johann.

Oh it's a DOS vector, see https://bugzilla.mozilla.org/show_bug.cgi?id=1122237#c12

I guess we'll solve that through your work on tab prompts, too. If you like We should make sure to test it. Do you think we should still file a separate bug for the insecure form warning? I can add a POC I made two years ago to https://eviltrap.site/...