Doesn't work on FF 30
Had to uninstall. I have a lot of toolbar bookmarks, and they run off the toolbar (which is fine by me). But this addon does 2 things that I dislike: 1) doesn't allow a way to access the "run-on" bookmarks in the toolbar (there's no drop-down) and 2) it removes the bookmarks folder itself (it just disappears from the far right for me).
Nice concept, but needs tweaking IMO.
The problem that you are facing can only happen if you enable "Use fixed width..." from the Options page. This is disabled by default in the latest version. Hope it'll solve your problem.
This is what I've been looking for for FF13* Does the job effectively.