Well, it's easy. Internet Explorer is a very old browser with not much novelty, besides tabbed browsing many years after Opera made it.
It doesn't comply to the standard, people have agreed to. MS makes up their own rules.
But all that being said, it seems that the Thirty Day Challenge recommends Firefox because of the plugins, so if you are going to follow it, you must use Firefox.
Changing habits are btw good for the brains.
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