shagmasterk said

This site somehow opened a new tab when I wasn't doing anything in FF

You may have ad / mal-ware. Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

For almost a year, an epidemic of Fake Update Notices have been popping up all over the place. https://support.mozilla.org/en-US/kb/i-found-fake-firefox-update

For all we know this is a form of malvertising and not caused by malicious software locally on your machine. To work around that please use an adblocking extension...

Try using uBlock Origin to block that garbage, https://addons.mozilla.org/en-US/firefox/addon/ublock-origin/

FredMcD said

shagmasterk said

This site somehow opened a new tab when I wasn't doing anything in FF

You may have ad / mal-ware.

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For almost a year, an epidemic of Fake Update Notices

Fred this is Not due to malware and 6-7 months is not almost a year.

shagmasterk said

Had all the right graphics, but the site obviously has nothing to do with Mozilla. I almost went for it.

This was why the scammers made the page this way to try and look somewhat legit and to try and distract you from the fact that you were not on a official *.mozilla.org page. Interesting though that the fake urgent update page they made for Chrome is more plain.