Bookmarks menu and select Manage Bookmarks. Right-click on the newly created bookmark and choose to edit Properties. In the Properties window put ‘gi‘ where it says Keyword, click OK and close the bookmark manager. Now, whenever you type ‘gi‘ and hit Enter key while in the address bar, you will go to http://images.google.com.
This is a nice way to minimize the number of clicks you need to perform in order to get to your favourite sites. But it can be troublesome finding unique keywords for your bookmarks. Solving this particular problem is the aim of the “Mozilla/Firefox Custom Keywords Directory” project. They also cover a bit more on what you can do with your bookmark keywords. Check them out.