flvplayer will not work in fullscreen mode. The following change fixes the issue for me.
in
mod/resource/type/file/resource.class.php
around line 492, replace the following line:

'width:"600", height:"400", majorversion:"6", build:"40", allowscriptaccess:"never", quality: "high" };'."\n".

with this line:

'width:"600", height:"400", majorversion:"6", build:"40", allowscriptaccess:"never", allowfullscreen:"true", quality: "high" };'."\n".