At present IE is the browser used by majority of the users around the world; infact its miles ahead of competition in terms of usage.
Now any new browser related technology cannot be used widely until its implemented by IE. Lets take SVG for example, supported by both opera and firefox, it is a fomidable player that can to a great extent change the face of our UIs, but due to the non implementation by IE, it still cant become a defacto standard.
So the company that leads the browser race will always have a greater say in terms of the standards that it wants to push through in the web technology side. Say tommorow Mozilla comes up with a new way of doing animations on the browser, a new language like html which allows for richer UIs and may be 3d object rendering, it would not be widely accepted till IE implements it.
I think google might has a similar plan with its chrome. Giving things for free to start with doent actually mean they are free. Eventually if you have a browser in the market that every one uses then you have a monopoly in defining how users will interact, how data will be trasmitted, what new things can be supported and all such other things.
So it really matters that Firefox win the browser wars, so that standards remain opensource and the power of decision lies with us, with the people.