It’s become quite fashionable to badmouth Microsoft, their proprietary extensions to Web languages, and their lack of standards support, but really they were just responding to Netscape. Way back when, Netscape was ruling the roost and doing unspeakable things to the infant HTML.
Netscape introduced several non-standard tags that only it supported, the most obnoxious of which was the tag (which ironically is still supported by Firefox), but they also were responsible for and and introduced the now-standard and . They took a lot of flack for it, but they used Microsoft’s now-standard response that they will support the standards as they see fit but continue to try to develop the Web into more than it was on their own.
And just as Microsoft has done, a lot of Netscape’s proprietary extensions ended up as part of the official HTML recommendation. But the fact of the matter is that Netscape started the trend and Microsoft, simply responding to the market leader, took up the cause and carried it into present day. So anytime you blame Microsoft for creating proprietary extensions or trying to “guide” the development of Web technologies, make sure you blame Netscape first.