Delicious Plug-In
As I did my add-on presentation yesterday, there was a discussion about how some people's Delicious add-ons seem to open different side menus, buttons do different things and such. Unable to answer any of the questions while doing the presentation (though searching for answers would have lengthened the presentation!) I came back and found a new delicious add-on waiting for me on my RSS feeds!
The new add-on works on both Firefox 3 and previous versions and has new functionality. You can jump to specific tags, the add-tag window is a little more friendly and modern, click the new Bookmarks button and you have instant access to your bookmarks on a sidebar.
So the final answer is that I have no idea why people's other delicious add-ons were acting differently, but I do know that this new add-on is worth downloading.