No it is not legit. The fake updates exe can install things like trojans, viruses or unwanted software based on past reports.

The desktop Firefox is not just for Windows as it is for Mac OSX and Linux also so .exe would not be an effective way to send out Firefox updates. The updates are done internally in Firefox with a .mar file or by download from mozilla.org like say www.mozilla.org/firefox/all/

Even if Mozilla were to use .exe for Firefox updates on Windows, they would be serving them from a *.mozilla.org url and not from random websites with weird names.

Firefox Popups Enable

Firefox Popups Malware

The following contents are guides on removing firefox-patch.js Pop-up from both Windows OS and Mac OS. Section A is for Windows OS Users, Section B is for Mac OS Users, please read the corresponding steps to delete firefox-patch.js Pop-up from your computer. Firefox-patch.js is able infected both Windows OS and Mac OS, thus our lab worked out different solutions for each system. Please read the the First Section if you are a Windows OS user; read the Second Section if your a Mac OS user.

Mozilla Firefox Patch Download

Jul 18, 2016  The 'Urgent Firefox Update' pop-ups are often miscategorized as a 'virus' or Trojan. In most cases, the 'Urgent Firefox Update' pop-ups are caused by a non-threatening component on the user's computer that may be a PUP (Potentially Unwanted Program) or adware, which may take the shape of a Web browser extension or plug-in. 2018-24 Security vulnerabilities fixed in Firefox 62.0.3 and Firefox ESR 60.2.2 # Fixed in Firefox 62.0.2 2018-22 Security vulnerabilities fixed in Firefox 62.0.2.