URL references such as www.ritlabs.com and firstname.lastname@example.org are automatically highlighted and "activated" as you type them in the message editor or as they appear in a received e-mail.
You can click on the highlighted URL reference to "launch" it. If the URL is a web (or http:) reference, it will open in your browser. If it is an e-mail (or mailto:) reference then a new message window will open with the address already entered in the To: header field.
Not all URLs are easily distinguished. In some cases, the only way of URLs can be clearly distinguished from other text is when using HTML. If you want to open a URL which hasn't been properly highlighted, you can select the URL manually, invoke the context popup menu (click the right mouse button or press <Alt+F10> or menu button on an MS Keyboard) and choose the "Open URL" option.
N.B. If you use Internet Explorer, you can press <Shift> while clicking the URL to open the URL in a new browser window without affecting any which may already be open.