Since Gmail has changed the Compose window to look like a small chat message box, many people were not pleased. Gmail took our words of frustration into consideration and released an update.
To use the new “Compose”, you just have to click the large Compose button, and on the top left of the New Message window, click the double arrows (middle icon) to view it in the expanded full screen mode. You can still get the popout compose window by shift clicking the double arrow icon.
If you want the Full Screen mode to be default, on the bottom right of the compose box (while in the full screen mode), click the arrow to expose more options. You will have the option to default to Full Screen mode when you compose. I didn’t notice this at first, so hopefully this will be helpful to some of you.