An add on for firefox or IE would only prevent firefox or IE from installing programs.. And it could be easily bypassed or stooped..
You could try pressing the windows key and S , typing in UAC and then turning the user account control settings to high.
Also, press windows S, type in smart screen, click change smart screen settings, click change smart screen settings again and make sure smart screen is on.
However, again the best way to do this ( and when used properly this is the best way to protect the computer )
Is to create a standard user account, and do most of your online activities from the standard account.. Its much much more difficult for viruses to invade your pc from a standard account because they wont have admin rights to run..
So as long as you keep your Admin account pristine, and use the standard account for most of your daily computer usage, thats truly the most effective setup..
Other then that, you can raise the user account control setting to max, and turn smat screenon.. Those two steps will g et close to what you want, without having to make a second, standard ( non admin account )
Senior Technician and Network Switching Systems Operator / Maintainer.