Hi Jason, welcome to PCHF.
Internet Explorer is more highly used, but only because it is the default web browser that comes with Windows. Internet Explorer is probably the most vunerable browser in terms of security than any other. Some may argue that this may be because it is the most popular.
Mozilla is a completely different web browser, based on Netscape with a much cleaner interface and more secure. There are features of Mozilla (such as tabbing) that Internet Explorer has only just started to take on board with IE7. There is a host of Mozilla extentions you can use and choose from which are very very handy. (
https://addons.mozilla.org/en-US/fir...type:1/cat:all)
There are many detailed discussions and articles you can find on-line which may help you decide which browser to use, for example:
Why Firefox Beats Internet Explorer - O'Reilly Windows DevCenter Blog