Youtube – YouTube keyboard shortcut for the previous and next video in a playlist

You can just hover over the video and an icon like this...

The top one, the clock, will add it to your "watch later" list

and the one beneath it with the three lines and arrow adds the video to your queue

You can do this directly from the feed while looking at YouTube videos when you hover over the video. This works int he new YouTube layout so if you are still using the old YouTube layout I'm not sure how that would work.

There is also three dots usually next to a video anywhere on YouTube and when you press it this pops up...

(Add to queue, Save to Watch later, Save to playlist, and Report)

You can press any of the three and it will add the video to a playlist

I finally found a solution. It works in Google Chrome only and it requires two extensions.

Install the extensions Remove Scrollbars YouTube Options

Set Youtube Options to the fellowing settings:

Play a playlist in YouTube and go to the browser fullscreen mode by hitting the keyboard F11 button. This is important!
The transition of the video's are not fluently, but it stays fullscreen.