In olden days, when you clicked on an e-mail link in your browser, it had to have an e-mail client to launch. That method doesn't work if you use a service such as Gmail or Yahoo Mail as your main account.
Firefox 3 to the rescue. Watch our video on how to do this tip, then come back here for the written steps.
Go to Tools and options (Firefox and Preferences on a Mac).
Choose Applications.
Search "mailto".
In the drop-down menu Choose Yahoo Mail.
What? You don't use Yahoo Mail? Thanks to Lifehacker.com for publishing the instructions for how to use Gmail.
Open your Gmail in Firefox.
You'll need this string of code to enter.
javascript:window.navigator.registerProtocolHandler("mailto","https://mail.google.com/mail/?extsrc=mailto&url=%s","GMail")
Press add application.
And now when you click an e-mail link, it will ask you which Web mail program you'd like to use.
Get a few more non-video Firefox tips at Webware.com.