Chrome: It's not hard to watch YouTube videos while you do other stuff online: just resize your windows and watch them side by side. But SidePlayer makes it even easier than that. You can watch a YouTube video straight from the page you're on.
Once you download the extension, you'll see a "Play from SidePlayer" option on every YouTube video. When you do that, the video pops out of YouTube and into a small player that follows you from tab to tab. You can close the YouTube tab, and the video will keep playing. You can also copy and paste the video's URL into the SidePlayer bookmarklet in your browser bar.
You can copy and paste YouTube URLs into the extension, too. It's an easy way to watch or transcribe something from YouTube from an entirely different window. You don't lose space in your current tab, and you don't have to worry about resizing everything.
Give it a try at the link below.