Windows only: Create, save and play back YouTube playlists (they’re even saved in classic Winamp M3U format) in your Firefox sidebar with Windows-only extension YouPlayer. After you install the extension, just open your YouPlayer sidebar to get started. From YouTube, you can drag and drop any video url from YouTube (like the search results page) and it’s instantly added to your playlist. Of course YouTube has got its own built-in playlist feature, but with the YouPlayer extension it’s easy to search YouTube and build playlists on-the-fly while videos are playing in the sidebar—making this ideal for building music playlists from YouTube. YouPlayer is free to download, currently Windows-only.