It sounds like you are getting a random named websites claiming to have a urgent Firefox update. '''This is not from Mozilla or the Firefox web browser'''. The fake firefox-patch.exe and firefox-patch.js files can install things like trojans, viruses, or unwanted software on Windows based on past reports if the user runs them. The way Firefox updates are done has not changed as updates are done internally in Firefox (with a .mar type of file) whether on Windows, Mac OSX or Linux or by download from mozilla.org like say www.mozilla.org/firefox/all/ You could try using a adblocker extension like uBlock Origin to block theses fake ads if you keep getting them. https://addons.mozilla.org/firefox/addon/ublock-origin/ Unfortunately this has gone on for a few months now with one or two new sites reported almost everyday. https://support.mozilla.org/en-US/forums/contributors/712056/ and https://support.mozilla.org/en-US/forums/contributors/712075

As for Firefox updates you are behind with Firefox 47.0.1 as [https://www.mozilla.org/en-US/firefox/48.0/releasenotes/ Fx 48.0 was released on Aug 2nd] and [https://www.mozilla.org/firefox/48.0.1/releasenotes/ 48.0.1 was released on Aug 18].