What's your browser of choice? Personally, I use Microsoft's Internet Explorer 7.0 (IE 7) at work, and Mozilla Firefox 2.0 at home\u2026but that's not really my preference. I believe Firefox is a better Web browser, if for no other reason than the add-ons available to IE7 users pale in comparison to those available to Firefox surfers, and I like to heavily customize my browser. However, I've been warned by my systems administrators and others that many of CIO.com's Web-based applications "don't play nice" with Firefox. I've also got a few war stories of my own that prove their warnings aren't for naught. Most notably, our content management system, which we use to enter in the majority of content published on CIO.com, doesn't like Firefox or any other browser that's not IE. That means I'm forced to use IE 7 for the majority of my Web-based work. \u00a0I'm used to switching back and forth between Firefox and IE, but the recent news that Mozilla's open-source Firefox browser reached the 400 million download mark has me wondering how much longer Web applications will be designed with only IE users in mind.How many of you use systems designed to function with Microsoft's IE, and are therefore forced into using the software instead of your browser of choice? This seems increasingly ridiculous--and frustrating--to me, as Firefox now commands somewhere between 17 and 25 percent of the browser market share, depending on which numbers you look at. The IT Productivity Center, a tech research group, says Firefox holds 17.4 percent of the market, with IE taking just under 64 percent. W3Counter, a firm that tracks Web metrics, found that Firefox has 24.4 percent of the market and IE has roughly 66 percent. An official version of Firefox was first launched in 2004 and less than six months after its debut, 50 million Web surfers had downloaded the software, according to SpreadFirefox.com. In another six months, the browser had been downloaded 100 million times, and a year ago Mozilla saw Firefox hit the 200 million download mark. So though Firefox's 400 million downloads don't mean that 400 million folks are using the software--according to SpreadFirefox.com, Firefox's community marketing site, about 1 out of 4 downloads translates into a regular Firefox user--it does mean that Firefox has proven itself as a true player in the space and that's it's not going away anytime soon. From SpreadFirefox.com: "Firefox has reached 400 million downloads and demonstrated that not even the world's most powerful companies can keep people from a better, safer, faster Web experience."To the end of that sentence, I'd add the following:"...unless, of course, the people use systems from those powerful companies that don't play nice with Firefox."