I've seen posts on this but no solution. I do not have negative margins in styles but always get scroll bars in auto sizing popups only in Firefox; IE8 works fine. (If this is fixed in RoboHelp 9, perhaps I can persuade company to upgrade, but doubt it.)
Here are IE and Firefox of same popup.
Using version 18.104.22.168. I checked on your site, but the information isn't solving the issue. If you have any ideas, I'd certainly appreciate it.