Rated 5 out of 5 stars
When upgrading to Firefox 4, I was looking forward to having a toolbar button for a bookmarks dropdown. However, I quickly realized that it wasn't going to suffice. After a bit of searching, I found this addon and it's exactly what I wanted. Once I noticed you can right click to open the sidebar, I was sold.
My only complaint is that the popup is a bit ugly. Adding a glass border would make it look better in Windows 7.