Helium is a floating browser window that allows you to watch media, browse the web and do much more while you stay productive. Your content will never fall behind your other windows even as you switch tasks. Helium supports a customizable translucency mode that allows you to simultaneously see your content and your work, without intercepting mouse clicks when it's translucent. You have the ability to click, drag, scroll behind your floating content.
Head over to http://heliumfloats.com and install the latest version of Helium. If you don't already allow apps from unidentified developers, you'll need to right-click and choose "Open" the first time you use the app (instead of opening the app with a single click).