How to get hold of the javascript alert dialog controls like ok button in FF4

Hi,
I wrote an extension for FF4 to traverse the DOM structure and to do
some actions on the controls in FF4. I wrote it using native C++
Gecko2.0 library. I am facing an issue in handling of the javascript
alert/confirm dialogs. They didn't seem part of the DOM hierarchy. Is
there any way to get hold of those dialogs and inside buttons
programmatically. Could any one please suggest me any suggestions/
solution.

Appreciate your help.
Thanks,
Madhu Tadiparthi