If you are using IE, any web based plugins / activeX plugins are put into this folder:
\WINDOWS\Downloaded Program Files
You can delete anything or everything in that folder and redownload them as needed. The windowsUpdate plugin is also in that folder. if you ever have problems with that annoying thing, just delete it from this folder and get it again.
Hijackthis is a tool that will allow you to see what's installed on your browser, as well as other key information regarding your browser in the registry. It's primary function is for the removal of spyware, but it would allow you to see what's installed as well.