MacOS – Make the green full screen window icon on Yosemite maximize windows

Click the minimize/maximize button a second time or press Control-Command-F simultaneously. The button can be green or grey depending on how you have configured the appearance under the General pane of System Preferences.

To resize window, simply double-click window bar.

The best way to do this that I have found is to put the cursor in the upper left hand corner and wait a second. The green button reappears (you also get the top bar back in case you want to do other things than change the view.) and you can click on it to get back to normal view.

The green button used to be just for "zooming" the window (at least that's what they call it in austrian systems) - it's what it does when it shows the "+"

If you use that function what it does is it makes the window just so big, that no scroll bars are needed (with the limitation that it can't make it bigger than your screen of course). That is the intended behavior, some 3rd party apps might not implement that correctly however.

In 10.10 Yosemite the green button is now used for switching to fullscreen. It will behave as in 10.9 if you hold the alt-key while pressing it (you will also see the + sign appear).