Yeeeeeesssss! Simple and effective just the way I like it. So convenient to find information in forum threads and tech sites, with a lot less button clicks than using the site's search button. I also use it to eliminate results on Amazon (with a - (minus) sign) because their search engine sucks.

I really like that I can choose where to search on the site too. We can do this on Google ourselves but this saves typing and button clicks. Thanks!

Definitely needs the option to add one's own search engines. Personally out of the five engines offered I use only one (DDG) whilst all my other search engines (among which well-known ones far more used than 'Ask' for instance) are not available with 'Search Site WE'. At this time I have to use another extension named 'SiteSearch' (only 3 users!) because it offers the option to use whatever search engine (given a correct search query), but without the possibility to search subdomains only.

needs the simple ability to change search engine on the fly, instead of hiding it in options.
also would be nice to have it understand search engines already added into firefox.