Why is Firefox more secure than Internet Explorer?

When I suggest that my customers use Firefox instead of Explorer, alot of them ask "why is Firefox more secure than Internet Explorer?" This post will try to give you an understanding of the difference between the two browsers.

Simply put, Explorer is tied to the Microsoft Operating System (aka Windows), while Firefox is not.
All versions of Windows (98, XP, Vista, etc) and all other O.S.'s (Macintosh, Linux, etc) have several parts; one of these is the File Management program. In Windows, the file manager is called "My Computer" or "Windows Explorer."
By clicking on "My Computer" the user is allowed to view, modify or delete any or all of the files and documents on the computer, including files necessary for Windows to operate; the user may also use Internet Explorer to view, modify or delete any file. This is a problem because if the user can do it while sitting at the computer, a hacker or malicious program can also do it through the user's Internet connection.
Firefox is not designed to access the computer's file management program ("My Computer"), which means that malicious programs cannot access it through the browser either.

So now, you might be asking "How does Internet Explorer let bad stuff into my computer?" It does this through a mini-program that websites can add to your browser, called ActiveX controls.
Back at the beginnings of the Web, when most people only had dial-up access, web pages were mostly text with a few pictures. Microsoft, in an attempt to make Web pages that were viewed through Internet Explorer look better, created little mini-programs that would automatically (and invisibly to you, the user) download into Explorer and make the web pages have bells and whistles and animations and all sorts of additional little things that made the web pages become more alive (this is called "interactive" or "dynamic"). This way web pages seen in Explorer would look far better than the same pages seen through Netscape's browser.
Over time, the bad guys on the Internet realized they could build their own "controls" and Explorer would automatically download and run them like any other program.

It was in this way that the bad guys were able to take over peoples computers. Because ActiveX controls are run through the browser(which if you remember, allows anyone to delete or modify files necessary for Windows to operate properly), most anti-virus programs do not recognize the malicious controls as threats and do not get rid of them.

Firefox is just another program as far as the operating system (Windows) is concerned; just like Word, or Adobe Reader.

This is why Firefox is more secure than Internet Explorer; because people or programs on the Internet cannot infect or control your computer without your knowledge.