I found link for make extension. http://www.codeproject.com/Articles/87465/A-Simple-XPCOM-Tutorial Using above link, I made a small extension which is only add two values and display. But this is working with old sdk (Gecko sdk which specifies in above link) only. It use Interface nsIGenericFactory which not available in latest SDK. Please tell me if any link will help me to make extension which will work with latest xulrunner and latest mozilla. Any Help will be appreciated. (Please excuse me for my English.) Thanks, Dinaz