Throttle Browser Extension by Firefox user 12180224

Control who can send you email. A cleaner inbox means a happier you. Throttle is a service that keeps your email address safe and your inbox clean. By seamlessly substituting random, unique email addresses for use online, it gives users control over who gets into their inboxes, for the first time ever.

The Throttle extension provides a button in sign up forms that allows you to generate unique email address to sign up with so you don't have to give out your real address.