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Finally, Firefox, for me, has been the best all-around browser for rendering myriad websites. It seems Firefox can handle anything
Firefox is really good, but their is actually a second reason. Webdevelopers used to have IE as their primary development browser (you had to and their wasn't much else at the time of IE5.x and early IE6). We all know what that caused.
Now Firefox has the webdeveloper-toolbar and especially Firebug add-on and it's cousins, which a lot of webdevelopers use. Firefox 3.5/3.6 has the largest market share. So the webdeveloper knows what a page will look like for the visitor. Also the organisation behind Firefox is really commited to developing a browser that follows all the standards.
Also no sane webdeveloper wants to use IE anymore other then testing things and seeing things fail. Every webdeveloper has a lot of hate for IE.
What is even worse, no webdeveloper understands (other then slow market convergence) why anyone wants to use IE.
IE is slow, very buggy, less secure and the company developing it, doesn't really want fix or develop it.
It is constantly trying to balance between 2 things, not to lose market share on the desktop-apps to the web-apps and on the other side not have IE loose to much market share in the browser-department.