You should check for malwares or adwares. Try running an antivirus software or even Malwarebytes, also check for unknown add-ons or plugins installed in your browser.

This is a malware phish site from a Ad. So you are getting a random name website page claiming to have a so called urgent update for Firefox and a prompt to download a fake '''firefox-patch.js''' file?. This is not due to malware on Windows like above post says. '''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, unwanted software or to download additional stuff onto Windows based on past reports if the user runs them. The Firefox 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/ Firefox '''48.0''' has been the current Release since Aug 2nd. https://www.mozilla.org/firefox/48.0/releasenotes/ 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