Setting scene to 100% browser

I have done this before but can't remember how to do it! Did a search for topic, found nothing, fooled with TW for an hour but just can't remember how I did it.
So, how do you get the scene to display at 100% of the browser? I have set the main window to 100% and repositioned/anchored everything and that seems to work fine. Just can't get the player/viewer/scene to play at 100%.

So what am I forgetting?

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Nikon D300, D3s, Nikon 10.5 lens, RingT105N+Footplate+MrotatorTCPs, Giottos MT9261 Tripod, Manfrotto 410 Jr geared head.

If you know the "secret" then everyday is a good day!