It used to be that if you wanted to zoom any window on your Mac to see as much of the content inside it as possible, you’d hit OS X’s green button in the upper left of the window.
As of OS X Yosemite, the green button turned into a “full screen” trigger, zooming any window out to completely fill your Mac’s monitor.
If you hate that behavior, here’s an easy way to get the original zoom feature without the full screen.