There are people who write malicious code that take advantage of ActiveX's ability to install software on your PC without you knowing it. Firefox also takes the W3C recommendations for coding standards to the extreme, it is completely compliant.
Firefox is also completely configurable. You can add plugins, and skins. You can move the toolbars around to whatever configuration you like. A Google searchbar is built right in too.
Some of the plugins you can get including the following:
- Gmail Checker
Weather Alerts
Web Developer Tools
Mouse Gestures
Download Managers
Foxytunes - The ablility to control a media player from within the browser