Today I discovered Bookmark Keys, and it was love at first key stroke. The plugin is pretty basic - it hardwires you bookmark toolbar to the keys Alt-1 ... Alt-9.
I'm using it to take frequently referenced/edited pages on my wiki, and make them a keystroke away.
Why this isn't built into Firefox is beyond me. But, I guess that's what add-ons are all about.
Speaking of bookmarks, Steve Rubel published a comprehensive list of bookmarklets. If you aren't using bookmarklets, you're really missing out. They are little chunks of functionality that gets treated as a bookmark. Let's say your looking at a page and would like to write a twitter post about. Rather than opening up twitter, you click the TwitThis bookmarklet, and you're work is done.
Ironically, my most frequently used, and oldest bookmarklet isn't mentioned. It's TinyUrl. You click their bookmarklet, and the page your looking at is turned into a tiny url.
His list is still a most excellent place to start to become a bookmarklet master.