Here’s a trick which shows you how you to tell Firefox 3 to launch Gmail to send your emails when a mailto: link is clicked.
1. Open Gmail in Firefox.
3. If you are a Google Apps user, use this code instead, but replace example.com with your domain name:
4. Firefox 3 will ask permission to add Gmail as default mailto handler. Click the Add Application button, as shown.
So the next time you clicked on a mailto: link in firefox 3, you will be presented with a screen similar to below. Choose Gmail, and select “Remember my choice for mailto links” to set the preference permanently.