Since I found this, I use it so much I don't think I could browse without it.

If you look at the properties of a bookmark, you'll see a field named ``Keyword''. This is never filled in on its own. However, if you do fill it in, you can create a shortcut for that bookmark. So if my bookmark to http://empeg.comms.net/ has the keyword empeg, then if I type empeg in the url field, it gets expanded.

But that's not the cool part.

If the url in the bookmark contains the two-character string `%s', then anything you type in the url field after the keyword (and a space) is inserted into the url in place of the `%s'. This means that you can type searches directly into your url field and not have to deal with the often lousy UIs of some sites.

Since I found this, I almost never touch my mouse for browsing anymore. Ctrl-PgUp/Dn switches tabs. Ctrl-L puts me in the url bar. Ctrl-T gives me a new tab. Ctrl-W closes a tab. Only when I have to deal with a web site's crappy UI do I have to touch the mouse. If only Mozilla would separate UI widgets and links for tab-ness (a la OmniWeb), I'd be a happy camper.

More info

Some of my keyword bookmarks:
http://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=%s
http://us.imdb.com/Find?%s
http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=%s
http://dictionary.reference.com/search?q=%s
http://freshmeat.net/search/?q=%s&section=projects
http://search.yahoo.com/bin/search?p=%s