How to get the bounds of a dome node properly even when browser is in different Zoom state

I wrote an extension using native Gecko SDK for firefox browser, where
I was trying to get the bounds of the dom nodes. I tried in two ways.
One by getting offset left, top, height and width and other way is
through by calling the GetBounds() on the accessible node of that
particular dom node. In both the cases I am getting the actual values
where the browser in 100% zoomed. But when the browser is Zoomed In or
Zoomed Out, still I am not getting the proportionally changed values.
Instead of that I am getting the values assuming 100% zoomed.

How to get the Zoomed values correspondingly changed dimensions of the
control programmatically when the browser is Zoomed in or zoomed out.

Appreciate your help.
Thanks,
Madhu Tadiparthi