Sorry, I wasn't clear. It does not search the information that Firefox stores like it does for Internet Explorer, such as cached pages and favorites, and only searches in your email if you use Outlook, neither of which I use. So basically to me it is good for just a few filetypes, such as text and Doc files.

I like the idea though. I did some more research and I found two programs that do similiar things, but are perhaps a bit more mature at this point in time and can search through more types of files.

Blinkx which looks like it is free and
X1 which is not free but looks good anyway