hi, this is a scam tactic that is trying to trick you into installing malware, so don't download or execute this kind of stuff just because of a popup or redirect on a website! updates are handled automatically by firefox so you don't have to download anything for that (and you can always initiate a manual check for updates in the firefox menu ≡ > help (?) > about firefox). we suspect this is coming form "malvertising" (=ads placed on legitimate websites that redirect you to this fraudulent message), so using an adblocking addon like https://addons.mozilla.org/firefox/addon/ublock-origin/ might also help with that. [[I found a fake Firefox update]]

Thanks! That's what I suspected. These tricks are becoming more frequent of late.