According to WebSideStory's latest statistics, released on January 12th, Firefox has taken an even larger chunk of users away from Microsoft Internet Explorer. They go on to state that "The U.S. adoption rate of Firefox... has nearly tripled over the past month." Firefox now stands at 4.6% while IE has fallen to 90.6%. Internet Explorer has now lost a total of 4.9% over the past 6 months!
Marketshare isn't really the issue, that is, not in the sense of FireFox becoming the majority browser (which I wish it would, but frankly doubt will happen). Rather, the real issue is for FireFox to attain enough of a marketshare, and take it firmly enough to hang onto it, that web developers can no longer ignore FireFox's existence. That will promote better coding, which benefits everyone.
FF has quirks mode, its not going to prompt anything
Apparently you haven't read all the posts here by people who are wondering why their sites break so badly in FireFox, and it turns out that their WYSIWYG editor was using IE-only code. That was me a couple years ago, and this very issue prompted me to start writing decent markup. I know of others who came to the same conclusion for the same reason. So the fact that FireFox has a pretty good quirks mode is still irrelevant; it doesn't support the proprietary MS markup and therefore will make people stop using the proprietary stuff if they want a cross-browser compatible site.
That's like saying my 2 year old niece is gaining ground on Yao Ming in height.
I don't know about you, but if my business lost over 5% of its worldwide market share in 6 months, I'd be worried. That's just me, though. And IE is already below 90% in OneStat's worldwide browser share numbers (WebSideStory is more business and ecommerce-oriented)
Anothe good thing about this is that it makes anyone who designs public sites for IE-only look seriously out-of-touch. Why would you want to turn away 1 out of every 10 visitors?