When you edit a page in full screen mode (on Firefox 29), you can’t see anymore the “Exit full screen” blue button

Steps to reproduce:
1. Hover over Edit and click WYSIWYG
2. Click on the "Edit in full screen" green button

You can’t press on the "Exit full screen" blue button, because you can’t see that button. Actually, you are not able to see any other button and the editor remains in full screen mode.