I concur it's crazy. Same thing happened with Internet Explorer. Back then, you could not have 5, 5.5, 6 together on one Win98. When installing later versions, they would replace earlier versions. But as a hobbyist I needed all to test my Web sites. The recommended work-around was VMWare. VMWare was not installable on Win98, so I tried Linux as host OS. That was the pivotal point that got me into my serious programming career.

Years later a hidden API was found out that made it possible to install the browsers in parallel. http://web.archive.org/web/2007/http://labs.insert-title.com... If Microsoft had documented that for the public, they would have saved Web developers thousands of man-years of work.