Standards have nothing to do with it. Browsers are supported on the basis of market share, nothing else. In other words, there's no chance that a sizeable number of people would be left without a working browser. Maybe we'd all be stuck with IE6 (and slightly crappy IE6 renderer-clones on Linux, like we have OpenOffice and KOffice for MS Office docs) -- but what would have been radically different about that? It would suck a little bit not to have tabbed browsing and AdBlock, and a few other amenities like keyword search might be missing, but would that change the web experience so much?
Besides, according to Wikipedia's market share numbers IE had over 90% of users during 2002-2006. I managed to rely on Mozilla and Firefox during that time period, so Firefox's success was not a prerequisite for alternative browsers to work "well enough."