Browser scaling - how to get original dimensions

How does one simply create a Textfield in Actionscript that has the dimensions of stage as seen in the html embed statement?

tf.width = stage.width or tf.width = stage.stageWidth

is no good as browser zooming has already scaled stage.width and stage.stageWidth, and then will scale the textfield - so a double scale.

This is ok if browser zooming occurs after creation, just not before.