Yes, I yelled in the title. It's that important! Mozilla urges users to update Firefox with file stealing exploit in wild | ZDNet From the article: "Earlier this week, Mozilla was notified by security researcher Cody Crews that a malicious advertisement on a Russian news site was exploiting a vulnerability in Firefox's PDF Viewer to search for sensitive files on users' local file systems. The exploit has been fixed in Firefox 39.0.3 and ported to its extended support release, Firefox ESR 38.1.1. Versions of the browser that do not include the PDF Viewer, such as Firefox for Android, are not vulnerable." This is something that everyone needs to do quite literally immediately. This was found "in the wild" which means it is an active, current, existing exploit that is on the Internet right now.