Robin19's comments about Firefox are right on. To an extent, they can actually be applied to just about any browser outside of Internet Explorer. The main issue that Internet Explorer users should be concerned about is security. It's literally a spyware and virus magnet. In its infinite wisdom, Microsoft decided to 'integrate' IE into the Windows operating system. That makes it possible for the user to download, install, and run software?without knowing it?simply by visiting a website. No other browser has this kind of operating system access, so by default a lot of security issues go away. Firefox, for instance, will make a user click on a button and confirm before a download occurs. It won't run an .exe file. That file will just sit on your desktop until you double-click on it. You can still get spyware that way, but at least you have several opportunities to either say 'no' or change your mind. If you find you do have spyware on your system, at least you have half a clue as to what might have caused it to get there. Another really cool thing about Firefox is that its developers are extremely conscientious about dealing with security issues. Microsoft has been known to leave severe or critical security bugs open for a year or more without fixing them. If a bug is significant enough, the Mozilla people will likely take care of business within a few days. Even better, I don't believe a Firefox security bug has ever actually been exploited. Mozilla offers $500 rewards to people who find and identify these bugs. Essentially, these issues are identified and fixed before anyone gets around to putting them into action. The rendering stuff is quite a bit less tangible to the average end user. But it's a big deal to webmasters. Web pages are written with various types of code, including HTML, CSS, and javascript. Web developers should be following World Wide Web Consortium (W3C) standards. The intent of these standards is to provide a degree of assurance that web sites will render about the same way in all browsers. The problem is that IE has a history of mangling HTML, CSS, and javascript. Because its Trident rendering engine is severely outdated, there's a lot of code IE doesn't 'know about'. Worse, there's code that IE simply gets wrong; it sees the code and does the wrong thing with it. Worse yet, Microsoft 'invented' a ton of code that isn't part of any standard and only works in IE. The irony is that Microsoft is a member of the W3C and has a say in the standards, yet hasn't made much effort to implement them. In short, the philosophical issue here revolves around getting a lot of the less competent webmasters to design their pages properly. If they're looking at their server logs and notice an increase in the percentage of 'alternative' browsers visiting their site, they'll be forced to 'expand their horizons' beyond that of IE and Windows.