It's an important and easy to use extension to Firefox. Just start your video, wait some 20 to 50 seconds to allow synchronization to be initialized, then click the three balls logo of the extension, and click the row where the word "streaming" appears in the open curtain-menu. Video DownloadHelper will start the conversion to standard .mp4 file warning you of the running process with a "1" over the three-balls logo.
It also warns you when your conversion is accomplished, so you'll find your complete .mp4 file under 'yourcomputername'/dwhelper.
Really one of the best downloaders, with recently improved easier interface.