Greezmo is an experimental Firefox extension developed by Gilad Kutiel that provides a simplified interface to search YouTube and make and control playlists of selected videos.
The interface is somewhat strange because of its size, location and the fact that it is overlaid over the content so you can switch tabs and the manager is visible at all times.
The left-most panel is for searching. Double click on the results (no thumbnails!!) to play it or press the add button at the top to add it to the current playlist. Playlists are nothing but bookmarks folders stored on a bookmarks folder called greezmo, a very simple approach that works neatly and makes it pretty clear how videos are organized.
The center panel is for playing and the third one is where the playlists are displayed. There’s not much to do there right now except removing and playing, no reorganizing at this time.
Control buttons to play, pause, play next and previous buttons are added to the status bar along with a button to show/hide the manager.
I would appreciate an option to open the manager in a tab, the ability to search other video and audio providers, a la Songza, and more visual hints (thumbnails at least) to be sure a result is what I think it is. But it is early on its development cycle and already a helpful tool for web video lovers.
Greezmo is an experimental add-on (awaiting for more reviews) available at Mozilla Add-ons.