All the major browsers support adding custom search engines. You just need to specify the URL template to do the search. The common format is to put "%s" as the search term. You can use it for any site, not just things that are considered search engines.

Firefox is a bit different, since you do it by adding a bookmark, and giving that bookmark a keyword. The other browsers I checked have an option under the search engine settings.

After defining the custom search engine, you just type "<keyword> <search term>" in the URL bar.