Youtube full screen doesn't work properly on yosemite Since my macbook is a 13" model, I like to use my entire screen when watching YouTube. But a problem has started.


When my Firefox isn't in full screen, and I click the full screen button of my video, Firefox goes to full screen mode (opens a new desktop and goes to full screen) and then shows the video in full screen. 
When my Firefox is already full screen, the video just opens in full screen as it should, but once I close the video, Firefox also goes out of full screen.


So I can't keep my Firefox in full screen if I want to watch videos in full screen. I can't keep it windowed if I want to watch full screen.

Also the constant going in and out of full screen of Firefox is insanely annoying since it takes a few moments for the animation to complete.

Anyone out there that has the same issues?
Just to confirm your observation on current version 38.01 of Firefox.

There are 2 types of full screen mode.

One is the Firefox it self in full screen mode. It will stay like that till you turn it off.

It does not look the same as the Video full screen. You can still see the Tabs. It is not correct that it will open the videos in full screen automatically, you still have to do that on the video it self.

The second mode is the Video full screen mode. It is controlled by the video player. In this mode the video takes truly the full screen and you do not see the tabs any more.

In full screen "video mode" all browser functions are disabled (not visible) thus you can not browse anyway.

Granted in your situation:

Firefox full screen -> Video full screen, when exiting video full screen also the Firefox it self will exit the full screen is what Firefox does currently.

That is (was) a known bug in Firefox.

One way it works better is to choose the Video player for YouTube. 

Switch from the HTML5 player to the Flash Player.