You can use the current URL bar for search. Either by settings or by using search keywords.

For example to search on Google "g search keywords", on Wikipedia "w epr paradox", Dictionary "d prometheus". Opera and Chrome have this too IIRC.

To search history "^ page keywords", bookmarks "* page keywords", tags "# tag words" (there are others, I blogged about them http://alicious.com/fast-bookmark-and-history-search-in-fire... or see http://kb.mozillazine.org/Location_Bar_search).