Just to let you know that the videodownloader plugin works with seamonkey, https://addons.mozilla.org/en-US/seamonkey/addon/2390. One thing, it's considered an 'experimental addon' and you have to setup up an account with mozilla to be able to download/install it.
Also for iDesktop.tv there is no download. It's a Web 2.0 app. You have to have scripts enabled in your browser, you use the search function to find what you are looking for, the videos are displayed as thumbnails with little icons at the top of each one, play, download, email, etc., but to use the download option you have to register, it's free, but maybe something some people don't want to do. One more possibility for spam.