It seemed people appreciated my last Firefox tip about deleting autocomplete entries. Here's another one.
If, like me, Wikipedia is your first point of call for just about any enquiry, here's a quick way to search for what you're after, without faffing about with search sidebars and the like.
What this tip does is allow you to type wp <search term>" in the URL bar and be instantly transported to the result of searching Wikipedia for that particular term. So type wp Eltham Palace and you'll be immediately taken to the page for the art deco masterpiece in South London.
To do this, create a bookmark with the Location set to http://en.wikipedia.org/wiki/Special:Search?search=%s&go=Go. Note the %s component, which will be filled with the search term. Put wp into the Keyword field of your bookmark. Now whenever you type wp followed by a space and then your search term, you'll go to the Wikipedia search.
Obviously this can be used for other searches. For example, I search the Internet Movie Database with http://imdb.com/find?s=all&q=%s&x=0&y=0. It's a brilliant way to search the sites you use all the time.
Update: Andy Owen points out a much better way of doing this. Right-click on any search box and select Add a Keyword for this Search... which then pops up the bookmark window. Much easier than my method, and something you could explain to mere mortals who don't understand URLs.