How to verify PGP signature with signing key using Enigmail in Thunderbird [migrated]

I received an email like this above:

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1  Because anyone can claim to be me. There's no validation of the user name or email address when someone posts a comment. While I do try to remove imposters, some may slip through. By signing my comments using this technique, anyone can independently verify that I was the author of the message by validating the signature. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (MingW32)  iD8DBQFFxqRFCMEe9B/8oqERAqA2AJ91Tx4RziVzY4eR4Ms4MFsKAMqOoQCgg7y6 e5AJIRuLUIUikjNWQIW63QE= =aAhr -----END PGP SIGNATURE----- 

And another email with the public key. How can I verify if the signature is valid using the Enigmail in Thunderbird?