Positioning works in tests but not in browser!

Hi guys,
I wrote an app that uses the stage.stageWidth and stage.stageHeight to position various elements. It works beautifully when I run the swf in the standalone player, but when I upload it to a site and view it in the browser the positioning is all wrong!
I don’t understand what’s happening.

Any ideas? Is there some property of the stage I’m not setting or something?
And why would the same swf function one way in the player and differently in the browser?!