I wish somebody would have told me about this feature long ago. Firefox supports keywords on bookmarks. I've seen that in the interface for many releases and never bothered to figure out what the heck it's for. I always figured it was for some sort of searching/tagging feature in the bookmark manager. I don't usually keep that many bookmarks, so I instantly ignored it.
Big mistake. They work like shortcut keys in the address bar.
For example, if you were to bookmark "http://weblogs.macromedia.com/mxna/index.cfm?query=byCategory&categoryId=1&categoryName=ColdFusion", you could add "mxna" as a keyword. Now, if you type mxna into the address bar, the bookmark gets loaded.
This is great for all those developer locations that you collect as you work.
Ok, I've got some bookmarks to tag ;)