Heading issue with the ePub file on Mozilla browser (add in - Epub Reader).

Hi

I am not able to get the specified font size of headings in the Mozilla browser (add in - Epub Reader) as compare to Adobe digital edition application. Could someone please help me find the way to get the same heading size for the same EPub file in Mozilla browser (add in - Epub Reader). I would also like to inform you that I created a CSS to generate EPUB from InDesign version 6 file,

Please find the relevant screen-shots attached.

Regards,

Arvind