Nifty, free Firefox add-on Email this! is great for anyone who wants to share Web page URLs with others via email software. When you're on a Web page whose URL you want to share with someone, click a button, and the add-in launches your default email client--whether it's a desktop mail client, such as Microsoft Outlook, or Web-based one, such as Gmail--creates a new mail message, and inserts the URL into the body of the message, and the title of the page into the subject line. At that point all you need to do is fill in the recipient's address, type in any message you want, and send off your email.
When you first install Email This you may be confused, because it may appear as if the add-in doesn't work; no buttons will be visible. You'll need to make them appear yourself. Right-click the Firefox toolbar, select Customize, and then drag any of the Email This icons to a toolbar. At that point, the icons will be ready to spring into action when you click them, although you may need to do some additional Yahoo Mail and Google Apps setup, although the documentation makes clear what you need to do.
You can add multiple icons, depending on how you want to send Web links via email. There are icons for Gmail, Yahoo Mail, Google Apps, and a generic client mail icon that will work with your default mail client. If you'd like you can drag multiple icons, so that you have a choice of which email service to use.
Once setup is done, Email This works like a charm. Soon you'll be sharing Web pages via email with ease.
Note: This program is donationware. It is free to use, but the author accepts and encourages donations towards further development.