Comment 2 for bug 1547770

Here are a couple of workarounds:

From the View menu in vinagre, enable "Keyboard Shortcuts". The F11 key will now toggle in and out of full screne mode. This had the disadvantage that some keystrokes or keystroke combinations aren't passed on to the remote desktop, which is usually the desired behavior

Hover your mouse pointer a few pixels below the top of the screen and move it slowly left and right over the area where the menu usually appears. Tooltips will pop out belonging to the buttons which should be displayed. Left-click when you see "Leave fullscreen".