3 has a cool new feature to allow you set default mailto handlers from the preferences. Here is how you can use Google Apps (GAFYD) as the default mailto handler.

1. In ’s address bar, copy and paste the following and hit enter:
about:config

2. Click “I’ll be careful, I promise!� when the warning appears

3. In the “Filter:� field, copy and paste:
gecko.handlerService.allowRegisterFromDifferentHost

4. Double click the found result to change the boolean value from false to true

5. In the address bar, copy and paste the following:
javascript:window.navigator.registerProtocolHandler(”mailto”,”https://mail.google.com/a/yourdomain.com/mail/?extsrc=mailto&url=%s”,”Google Apps”)

6. Replace “yourdomain.com” with your own Google Apps hosted domain and hit enter

7. Click “Add Application� when it asks you a question

8. go to Edit > Preferences > Applications > mailto

9. Choose “Use Google Apps�