All paying Firecracker members are eligible to refer friends, and receive rewards for spreading the love. You'll see a "Refer" icon on the left-hand navigation panel, which will also break down the rewards you can earn for inviting friends to Firecracker. We can make exceptions for users who are under long term unpaid accounts and who are members via school accounts - just write to us at firstname.lastname@example.org and we’ll help you get set up.
Members on a regular free trial of Firecracker are not eligible to participate. Here is an overview of our referral program rewards and rules: http://learning.firecracker.me/firecracker-referral-program-faq