If you're still using IE, I feel it's time for you to ask yourself why. Firefox is a cross-platform internet browser that can be used on a PC, Mac or Linux. I've been using it for years now and I've never looked back. Back when I first started to use Firefox, some sites that I visited weren't compatible with Firefox (because they weren't W3C compliant, even though they should have been) and I'd have to open them in Internet Expolorer but I virtually never have to open Internet Explorer these days as most web designers and developers I know use Firefox.
So why is Firefox better?
Firefox has a very user-friendly interface. Common toolbars (like the Google toolbar, for instance) are supported. You can save your passwords. Your bookmarks are saved as an HTML file instead of "Favorites" so it's super easy to export them, import them or whatever you like.
One reason for this might be that most users have Internet Explorer and therefore it's more profitable for crackers to find exploits that they can hijack in Internet Explorer. IE is notorious for it's security holes and once a problem is discovered, it's up to Microsoft to work on a fix for the bug and they then release it on "patch Tuesday". By contrast, Firefox is Open Source, which means that the source code is freely available and so once a vulnerability is discovered, members of the community can create a patch for the issue and close the vulnerability fast. You can set Firefox to check for updates automatically so your browser is always kept up to date. In essence, it's easier to avoid spyware and malware when you use Firefox.
Built-in Popup Blocker
Firefox has a built-in popup blocker to stop annoying pop-ups from sites. Bliss.
Okay sure, IE now has tabbed browsing in the newer versions but Firefox had it first. It's much better than having eight browser windows open. Firefox will still let you open a web page in a new window if you'd prefer to.
If for some reason a site crashes your browser, the next time you open Firefox it will ask if you want to restore your session or start a new one. If you restore your session, all your tabs will load with the pages you were browsing. This has saved me countless times.
There are many extensions available for Firefox that you can use to customize your browsing experience. Extensions are available for everything from safer shopping on eBay to web developer extensions that help you validate your code. There are extensions for most imaginable uses, from stopping autoplay of videos on websites to downloading full photo albums from Facebook, cookie and script control, parental controls, Livejournal add-ons and even ToDo managers.
My favourite add-ons are FireFTP, Google Toolbar, HTML Validator, NoScript and IE View Lite (which lets you open an IE tab within Firefox, great for web developers and designers).