How do I set Gmail as default Email Client in Firefox?

1 Open Gmail in Firefox 3.
2 In Gmail tab, paste the following JavaScript into your address bar:
javascript:window.navigator.registerProtocolHandler("mailto","https://mail.google.com/mail/?extsrc=mailto&url=%s","GMail")
3 Firefox 3 will ask for permission to add Gmail as a mailto handler. Click "Add Application".
4 Click on this example mailto link example@example.com and Firefox will ask you what application you want to use, and allow you to store your preferences permanently.

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Thank you for that