hello, this is a phishing tactic that is trying to trick you into installing malware, so don't download or execute this kind of stuff! updates are handled automatically by firefox so you don't have to download anything & if you want to download the full firefox installer always do it directly from mozilla.org. you might also want to run a full scan of your system with the security software already in place and different tools like the [http://www.malwarebytes.org/products/malwarebytes_free free version of malwarebytes], [http://www.bleepingcomputer.com/download/adwcleaner/ adwcleaner] & [http://www.kaspersky.com/security-scan kaspersky security scan] in order to make sure that there isn't already some sort of malware active on your system that triggers these kinde of false alerts. [[Troubleshoot Firefox issues caused by malware]]