Trouble with full screen mode and focus shifting to other programs

Hi. I've been using Opera (version 11.52) to catch up on my TV while doing some work. I'm using a dual monitor Mac setup (Snow Leopard), so the Opera video is on one screen and the productive stuff on the other. For a while I could launch the video, choose full screen mode, get a dialog that asked me something about fullscreen mode, other applications, and focus (the exact text of which I forget, but that I believe I answered no to), and then have the video play in full screen on one monitor while I happily draft away in AutoCAD or whatever on the other.

Well, last time, I checked the box about not asking me again or remembering the setting or whatever it says, but I apparently chose the other answer this time because now whenever I switch to another program on the main monitor, the video leaves full screen mode on the second monitor. And because I checked the don't ask me again box, I'm not being given the opportunity to fix this. I can't find a setting for this in the Preferences.

How do I get back the ability to watch video fullscreen when Opera loses focus?

Thanks.