Freemake Video Downloader (http://www.freemake.com/free_video_downloader/) ver. 2.1.2 adds two new sites to the list of supported resources: Howcast.com and Movieclips.com.
The downloader plugin is now functioning in Firefox 4 browser. You can easily convert videos from YouTube to MP3 directly from your browser. The problem with downloading from MTV Network sites is also fixed.