Hackers continue to find and exploit security holes in IE. Many of them take advantage of Explorer's ActiveX system, which lets Web sites download and install software onto people's PC, sometimes without user's knowledge. ActiveX was meant to make it easy to add the latest interactive multimedia and other features to sites, but instead it's become a tool for sneaking spyware onto unsuspecting PCs. Firefox avoid ActiveX and other well-known infection paths. You can configure it to automatically download most files when you click on them, but not .exe files, which are runnable programs and since .exe files could be viruses or stealth installers. FIrefox simply aren't hacked into that often as IE. Internet Explorer is used by 95 percent of the world. Firefox's users add up to 2 or 3 percent at most. Which browser do you think people are most likely to hack?
Firefox also adds a productivity feature that Explorer has never gotten around to and that is tabbed browsing. This is cool stuff. You can open several Web pages in the same window and flip through them as tabs, similar to those used in some of Window's dialog boxes. If you're in the habit of opening a bunch of news and other web links all the time or clicking on several Google results from the same search, tabbed browsing makes it more efficient and organized than popping up a whole new window for each link.