One of the most ballyhooed differences is security; IE has been famously prone to flaws, while Firefox has remained largely outside of the virus and worm threatscape in part because it has fewer flaws and in part because it has fewer users and is not yet attracting the attention of hackers. That's subject to change, of course, as more people adopt it. Firefox has some differences that truly make it more secure, however. For example, it doesn't automatically load ActiveX controls, tiny programs that have been the cause of many of IE's security holes. Pros. Better security and the ability to precisely customize it to your wants and needs make Firefox a pleasure to use. Cons. Since Firefox doesn't automatically load ActiveX controls, there are some pages that simply won't load in the browser, or won't work properly. For these pages, you'll have to open IE. Where to get one? The browser is available for free from Mozilla's Web site.