Doesn't work for me.

This causes videos to play in theater mode as opposed to default view. It does NOT play videos in fullscreen.

This is what I wanted! Easy to use, does what it's supposed to, i.e. automatically play YouTube videos fullscreen.

v1.1 worked well and I give it 5 stars. The v1.2 update caused some trouble for me in that sometimes the video don't auto fullscreen. I still recommend this extension as I have a 32" OLED and I often forget to click fullscreen leaving static graphics on the screen.

Edit: Developer response