Hello swethasankaran,
I am experiencing the same issue as you did with the rich text box not auto expanding in IE. It works in Chrome, and firefox. In IE, the table row will expands, but the actual rich text box will not. It doesn't work for me regardless of what I do with the ribbon. I am using Office 365, SharePoint 2013, and InfoPath 2013. In fact, I can't even use the rich text box on this site unless I put IE11 in compatibility mode. Putting IE11 in compatibility mode doesn't solve the auto height issue on my browser form.
In addition, if I remove the InfoPath form from the list, the rich text field height auto adjust just fine. But when I place the InfoPath form on there, it does not.
Any ideas? This is extremely frustrating how it works in chrome and firefox. Why is it that two Microsoft products do not play nice with each other?