If Firefox works fine, I think you should simply consider to make CSS more Chrome friendly because even using Frame via ActiveX you won't have DOM, so no canvas, and speed, as I said, won't be better.
4 years the same application, I think it's time to upgrade/maintain it, isn't it? Your company will be the only one with benefits and it can easily migrate to other browsers or update platform/Operating System when it will be time to do it.
I don't get applications that would like to be the same forever, this is not IT, imho, and IE6 support, as well as Win98/ME/2000 is not acceptable from security and performances point of view.
I know it's probably not your decision, but there are few options right now and my suggestion is: make your App more Web Starndard, and you'll be able to use Chrome, Safari, Oepra, Firefox, whatever, now, and for other 4 years :-)