https://addons.mozilla.org/en-US/firefox/addon/add-custom-search-engine/
It allows you to add search engines to your address bar, so you can type in the term(s), click the icon, and search that site. I've added LibriVox, Internet Archive, and HathiTrust this way.
Basically, figure out what kind of search you want by DOING a search, then grab the URL of the search results and plug 'em into the add-on, replacing the search term(s) used with %s. Some sites will suggest an icon; if you're savvy, you can use a screen capturing function to make an icon for a page that doesn't suggest one. (I used Snipping Tool to grab the LV icon from the forum here.)
SUCH a time and sanity saver for me!
