You can easily add a "search engine" to firefox for almost every site that has a search form: just right-click into the search field and select "Add a Keyword for this search...", give it a name and a (preferably short) keyword.
Now you can type "<keyword> <search query>" in the address bar and firefox will open the search results of that site. I use it frequently for dict.cc and wikipedia, where this approach works very well. Search forms that are submitted by POST are harder or impossible to use this way.
-housetier
True, that's quicker and I should have mentioned that. Lately I've had a preference for having each search available as both a search plugins and a keyword because of
certain add-ons that work only with the search plugins. One disadvantage of this is that sometimes I have to
create the search plugin myself, like I did for
DonationCoder.