Is it possible to make an extention which makes video on YouTube fullscreen once play button is pressed and back into window once paused?

Expand View does not expand to fill the viewport, at least when the browser is full screen. And full page view overflows the viewport.

Also, when clicking on video search results within the YouTube site, it always takes me to a posting by zFrank instead of the selected video.

It does what it says it'll do but there seems to be some kind of error. With this add-on enabled, putting anything into the Google search bar takes me to whatever I was searching for's website instead of the Google results page. I've disabled this add-on and tried a search again and things went back to normal. So it's this add-on that causes the Google search to do this. Please fix

Great but slows youtube bandwith down a bit.

Never had a problem with it, it's pretty reliable :)

I just wanted to enable theater mode by default and that's it.

I have never had a problem with the addon, but Avast gave a popup that says that this addon has a bad reputation and recommends I remove it.

You might want to check on that, I couldn't find any information in their forums but I won't be the only one getting that notification.

Works as promised. No regrets.