When you click on an email link on a webpage, Firefox will normally open your operating system’s default mail program (EG; Windows Live Mail). If you would prefer to use a different mail client, you have the option to change this setting. For example, I prefer to use Gmail.
In Firefox, go to the Tools menu, and select Options.
Go to the Applications tab, and scroll down to find mailto in the content type column.
Click on the corresponding action to select a new setting from a drop down list.
You can choose to have firefox Always Ask you which mail client to use, select a default program like Windows Live Mail or select a default webmail client like Googlemail or Yahoo! mail.
Select whatever option you prefer and click Ok to close the Options window.