Implementation in a panel is not a great idea since it re-checks all bookmarks each time you open it and the results don't cache. The list keeps scrolling to the top as it returns results so you have to wait until it's all done... and forget about viewing another website while it works since you have to start over if you leave the panel.
I just updated the add-on the version 1.1, which moves from the panel to a normal webpage. You still don't get caching after you close the tab, but I don't think that would be really useful.
