"Chrome allows web services to ask if you'd like to use them to open certain links. While most links generally take you to another page, some links can open programs and perform other actions. For example, mailto: links can open your email program and webcal: links can add events to your calendar program. These links are referred to as protocols and the programs they use are called handlers. Many web services these days, including Gmail and Google Calendar, can act as handlers," explains Google.
To edit protocol handlers in Chrome, open the settings page, go "under the hood", click "Content settings" and then "manage handlers". Another option is to open a new tab and paste this in the address bar: chrome://settings/handlers. By default, you'll see an almost empty page with no active handler. You can add protocol handlers from the sites that support this feature: Gmail, Google Calendar (and other services in the future).
Chrome is a little late to the party: Mozilla added support for protocol handlers in Firefox 3, back in 2008 and you can set Gmail as default handler for mailto: from the options dialog.
{ Thanks, Kevin. }