Shined up real nice.
Search YouTube without interrupting the video, by loading the search results in the related video bar
Update 2.0.0: This script now works on both Classic and Material Youtube!
Note: Doesn't work with Material Youtube (yet)! (Script to automatically restore classic youtube)
If you also want to be able to create a queue with videos to play after your current video has finished, you can use Youtube Play Next Queue.