This is what happened to me.
Awww no!! Don't tell me the "coconut wireless" (TWC Hawaii) strikes again!!
I think I know what is going on with your browser window. When you are looking for the red, yellow,green buttons, they will appear after you hit esc. If you hit the green button again. the window will again go to full screen. It seems you can not expand the window to full screen with the finder tool bar and so on, visible. I want to see my system status, so I generally use the bottom corner grab and put it where I wish. I can NO longer do that.... it bounces back to a default window size, I DO NOT like that. But it is what it is. I do not particularly like the iTunes windows. I think they are pretty lame.
I preferred the graphics from the other OSs. See if you can figure out the window size with the esc button. Not the force quit, although if you need to do so, use it like the person mentioned.
I have a friend whose network has had bugs post Yosemite update and now Pandora won't work on his iMac. His selection for slide show whilst his computer is in screen saver was changed to the NatGeo default which he has changed several times, but it wont seem to let him command his machine, and goes back to NatGeo. He's a techie, and is quite confused.