I brought my father a new PC and three months later had to do a complete windows reset because he does not know how to browse the internet. He infected it with malware, causing software errors, and causing some Win 8 files to be corrupted where Blue Screens of Death started to appear. All but one malware was removed and the unremoveable one was one of those persistent ones that keep reinstalling itself as a browser plugin. What I need to know is how to prevent firefox from being able to download and install plugins. I setup a basic secondary account (a standard user user, no admin privileges), setup the windows 8.1 family filter and the internet security software's own family for two layers of protection, but I can not prevent firefox from downloading/installing new plugins. How do I make it impossible to add plugins unless permission is granted? The fact that firefox (I use 29.0.1) can potentially install plugins when the user account I setup blocks software installation is a security risk for me.