UserLand's upcoming Pike product is going to integrate the IE HTML control on the Windows side. It sounds like the Macintosh version of Frontier won't have the same feature.

Here are some links that might help them out...

MacOS 9: HTML Rendering Library (this engine probably doesn't have all the features they need)
ActiveX SDK for the Macintosh (outdated, but would explain how to use the IE 3 and higher HTML engine in Frontier/Mac)
Mozilla

With UserLand's numerous contacts inside Microsoft, I'm sure they could find someone who could explain how to integrate IE on the Mac with Frontier to get the same affect as what they're doing with Windows. I'm also sure Microsoft would be happy to see UserLand using their engine... .

At this point I don't care whether they use Mozilla or IE, but I'd love to see Pike have feature parity across platforms!