For a surprisingly long window of time, IE Mac was the best browser around. Apparently, it did not share a code base with Windows IE, which explains why IE Mac had all the features people were drooling over in 2001 like full PNG transparency and good CSS support. PNG support even included color correction, and IE Mac did not suffer from the "box model" bug that affected IE on Windows.
I think the Mac version of IE had something like 99% compliance on the first Acid test, before other browsers had robust CSS support. You could even find a copy of the Acid test in an easter egg in the browser.
It was a fantastic browser at the time, but didn't align with Microsoft's future interests and the development team was reassigned.
For all the woe brought upon the web by Internet Explorer 6, the "box model bug" is indeed the one thing it did right. It took far too long for everyone else to admit the error and move ahead with the box-sizing CSS spec.
In 2001 I, for the first time in my life, had access to Macs running Mac OS 9. While I didn't like the operating system much (I was using Linux and Windows at home, the idea of having to assign memory to application manually felt so 80s) I instantly fell in love with IE for Mac. Back then, in PC land, Netscape Navigator and IE 5.5 were the dominant browser, and IE for Mac supported all these fantastic CSS properties that I knew about, but that I could not use in NN4 or IE5.5. I spend hours buliding pure CSS websites without images, simply utilizing unicode fonts, and CSS properties. Ah, those were the days.
Unfortunately it had the most annoying bug in that it did not reload CSS files. Back in the day, I developed with a text editor on mac PowerBook and after changing one CSS statement, I had to close the browser and restart it.
Ehh, IE5:Mac may have been better than IE5:Win, and yes, its CSS and PNG support were ahead of its time, but it was still IE5.
IE5:Mac didn't have support for a lot of things IE6 had that we now consider standard, like :hover for links, for..in, Array.prototype.splice, XmlHttpRequest, contentEditable...
I think the Mac version of IE had something like 99% compliance on the first Acid test, before other browsers had robust CSS support. You could even find a copy of the Acid test in an easter egg in the browser.
It was a fantastic browser at the time, but didn't align with Microsoft's future interests and the development team was reassigned.