The extension works both on the search portals’ main sites, as well as through a browser’s omnibox (in the case of Firefox) or browser bar (in the case of Chrome). (The “search from everywhere” feature is still in beta.) Disconnect says that it has applied for patents to protect the proprietary way in which it does this.
I like this as an option, but honestly, the fact that google is tracking me means that I get personalized search results that tend to be more relevant and therefor, more valuable. This isn’t the case for everyone though, and having a nice and easy option like this is a great thing to have available.