GoogleTube is a Firefox add-on with many cool features for YouTube users. It acts as an independent player for YouTube inside Firefox.
After installing this add-on (& restarting the Firefox, of course!) you can notice its small icon on the status bar. Click this icon to launch the player. This player always stays on top, and can be dragged anywhere. The player has search function to search YouTube videos. You can also minimize it to a small box. The player can be resized easily.
GoogleTube has another useful feature — it enhances the video results on Google, Bing and Yahoo! search.
You can see options to watch the video directly, download the video (in flv format) and video information. :)
Hence, GoogleTube is the coolest Firefox add-on. Its player helps you to see YouTube videos while working in some other tabs.