Would this do?
This Extension allows you to create, use and manage your own Google Custom Search Engines right from within Firefox.
Once you create these engines you decide which websites are covered and which not, how they rank and so on. If you don't change anything, your Google Custom Search Engine will be more or less a normal Google Search.
You can integrate your own favourite search engines into Google using customizable refinements - so, if you would for example like to search craigslist from within google with just a single click, go ahead and integrate it if you wish so.
Another new option is to add rewrite refinement labels - these can for example be used to exclude all shopping related searchterms from a search - with a single click from your Google Custom Search results.
Once created, the Google Custom Search Engines can be used by anyone - no login required. They can easily be integrated into your own website or blog.