Setting up Gmail as your default email client in your browser
Google enabled you to use Gmail as your default email client while clicking on email addresses using their desktop notifier app.
You can actually set it up for your browser itself by adding a new protocol handler.
This seems to work in Google Chrome, Mozilla Firefox and Opera.
Here is the code that you need to run in the JavaScript console of your browser while on Gmail:
navigator.registerProtocolHandler("mailto",
"https://mail.google.com/mail/?extsrc=mailto&url=%s",
"Gmail");
Mozilla Firefox and Opera users can actually edit this setting right from their preferences.