margin-right in iframe

Hi there!
I have some problems with right margin on firefox, when im trying to display WP in iframe…there is strange gap.
Firebug in firefox shows that some margin-right style exists on “content-body” div… if I set it to 0 – gap disappears, so i know that problem is in that margin, but i can’t find it in any *.css
Was it generated by WP? where i can change it then ?

in opera it’s ok

screen here http://img62.imageshack.us/i/screenzz.jpg/
link neon-mind.com