I just installed this Firefox add-on (by Yahoo! Inc.), which actually allows to integrate your del.icio.us account into your Firefox profile.
Well, it’s quite straightforward so I won’t bother getting into the details, but it’s absolutely worth a try.
So far I used to use another extension which just allowed the user to tag a page and add it to his del.icio.us bookmarks: the feeling I had before was that my del.icio.us bookmarks were just separated from my Firefox bookmarks (and they actually were). Now I really feel they are a single, integrated set, since I can browse, add and search links in Firefox.
Some months ago I actually thought having such an extension would be nice, glad to see guys @ Yahoo! worked on it. 
Dude, try “integrate”-ing with this addon and see what you got. All your tags will get messed up !!
If you’ve anything else to say, please post. Eager to read that.