This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Firefox, and other real browsers, use the standard Event instance as defined by the W3C. IE, on the other hand, uses its own proprietary layout. You need to accommodate both (or use a library like jQuery which normalizes the event object).