So, what's the big problem with that? The only real trouble was that the browser plugin that was required to run the 3D graphics inside of the browser was only ever created to work with Firefox and Internet Explorer. If you used Opera or Safari, you were out of luck. Chrome hadn't even been created yet, but no support was added for it either, when it came out.
To add to this, the graphics engine was running on Direct3D|DirectX. Now, don't misunderstand me, DirectX is great graphics technology. The only drawback is that Microsoft only makes it for Microsoft. (What I mean is that you can only use it on Windows, XBOX, Windows Phone etc.) Now, if you were only writing a game or something, the fact that it only runs on Windows isn't a problem, but if you're a great feature of a public service that people on Macs or Linux would like to use, then it becomes a big problem. (OpenGL is the graphics library that Macs, Linux, and game consoles like the Wii and PS3 use.)