This extensions lets you use tabs to make a temporary video playlist. When active the extension will switch to the tab to the right when a video finishes. When that tab's video finishes it will switch to the next and so on. By using the middle mouse button you can very easily line up videos you want to watch.
Note: This extension only works with the HTML5 player, make sure you have it at https://www.youtube.com/html5 .
Videos featured in the screenshots and video were made by vlogbrothers (https://www.youtube.com/channel/UCGaVdbSav8xWuFWTadK6loA)