The fastest Youtube video saving technique
The problem with the VideoDownloader extension is that once you click the "save target as" button provided, the whole video is downloaded again, even if a complete copy of the video is already in the browser's cache, a situation that would be true most of the time if you are used to watch the whole video before deciding you want to save a local copy for offline play.
Now you may ask, how to find the complete copy of the video in your Firefox cache if you don't even know its file name? Well, there's an easy way to know which file name the copy was saved with and for that you need to install a popular Firefox extension called AdBlock, which is really meant to block pop-ups and and banner ads.
Once Adblock is installed, go to the page containing the video to be saved and play the whole video or make shure that it is fully cached --the color of the timeline bar should be red all along. If Adblock is properly configured, you will see a tab titled "Adblock" afixed to the upper right corner of the video display area. Click on this tab and copy the code after the last forward slash from the address displayed in the pop-up text box.
Next, you need to install another Firefox extension called CacheViewer, which provides a very powerfull way to explore and filter Firefox's cache. Once, CacheViewer is installed type the code you copied before into the search box and after a couple seconds you'll get a list of matches; the one with the bigger file size is your local copy of the video. Just save it with a .flv extension and enjoy playing it with FLVplayer.