Based on the page you describe, that's a malware installer which infects the Windows registry, so good thing you did not install. Unfortunately, these phishing sites pop up on a new address every day so the built-in bad site blocker cannot keep up. If you right-click the Back button on that page, can you see what site it launched from? Often it's a popular site, and the redirect is served through an ad. Accordingly, if you've never considered using an ad blocker, you might consider it. This one has a good reputation: https://addons.mozilla.org/firefox/addon/ublock-origin/ See also: [[I found a fake Firefox update]]