There’s no reason for anyone to not have more than one web browser installed on their computer. Different browsers are good for different things.
For instance I prefer to use Google Chrome when I’m just surfing for the heck of it. I like how simple it is and has all the features I need without having to install a lot of addons.
My significant other, who is into Facebook, Youtube, Twiter and many other networking sites, prefers to use Flock, which has built in features that make this easier.
Also to look out for iss Oprah which is the most popular browser for cell phones, and Maxathon the most popular browser in China. Mac users rave about Safari and you can get it for PC too. Zac Browser is built for children with Autism. The point is there are many browsers out there. Not just IE.
Now if you’re working on websites then you really should use Mozilla FireFox. It was practically built for it. You should also have other browsers to test on. No two browsers will show your websites exactly the same without a lot of work, and they probably shouldn’t but you should at least get to know the differences.