Here are some stats that recorded the browser hits to one of my new sites after a month or so of air time. This cut compares IE hits vs. Firefox hits. As you can see, IE is apparently far more popular than Firefox.
As for my personal opinions, I have perspectives to offer. For a user, I commonly use IE myself. It has a few glitches every now and then, but it certainly does what I need it to do. Firefox works great too.
From a webmaster's perspective, Firefox is an obnoxious, picky, stubborn piece of s**t. I like making my pages look JUST right. When I get my pages looking like works of art in IE, it is almost certain Firefox will have a problem with it somewhere. This is also true in the reverse in cases where I work on pages in Firefox and later view them in IE. Those two browsers just can't agree. Personally, I give priority to the more popular browser.