# On the menu bar, click the Tools menu and select Set Up Sync. The Firefox Sync Setup window will open.
# Click I Have an Account.
# Since you're not near the device with Sync already set up, click the I don't have the device with me link.
# Sign in to your Sync account:
Enter your account email address
Enter your password
Enter your Recovery Key
Then click Continue
# You will see a Setup Complete screen. Click Done to complete adding this device to your Sync account.
If you don't have the Recovery Key, I'm sorry but you are out of luck. The data that you send to Mozilla is encrypted by it and it can't be recovered unless you use the key that, for privacy reasons, is never shared with Mozilla.