This week's book giveaways are in the Refactoring and Agile forums. We're giving away four copies each of Re-engineering Legacy Software and Docker in Action and have the authors on-line! See this thread and this one 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).