MALWARE!! Do not install.

According to how your Firefox identified itself to the forum, you already have the latest version of Firefox (47.0).

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

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.

Thank you!