When embedding a video to an article with eZ OE (through "custom tags"), there's an option "allow full screen" that doesn't make any difference.

disabling the online editor we get,
with "allow full screen" enabled (checked):

<custom name="video" custom:width="560" custom:height="340" custom:source="http://www.youtube.com/v/fO0ixUxDH14" custom:allow_script_access="always"></custom>

with "allow full screen" disabled (unchecked):

<custom name="video" custom:width="560" custom:height="340" custom:source="http://www.youtube.com/v/fO0ixUxDH14" custom:allow_script_access="always"></custom>

They are exactly the same, and the full screen doesn't work either way.