It's an opensource "metasearch engine" that aggregates other search engines (you can see which ones on each result), but anonymizing everything. At least, that's what they say. No idea yet about how good it is, I still need to test it more.
@pybonacci@marcelcosta You don't need an extension to add a search engine to Firefox: open the main page, click on Firefox's address box and on the bottom of the menu you'll see a list of all the search engines set for the browser, together with a button to add the current page to the list of search engines. Finally, go to Firefox settings and under Search options, pick the new search engine as default. After that, just type on the address bar and Firefox will use the new search engine.