Yes, after you revoke your key you can still decrypt messages sent to you encrypted with that key.
Note that you are also able to decrypt messages sent to you with the revoked key after the revocation. In fact, even if people aren't supposed to use that key (GPG/Enigmail will not allow to use a revoked public key to encrypt a message to someone), many of them could still have your public key when it was still valid and haven't refreshed it since then.
You should send to these people your new public key and your revoked old public key so they can update their keyring; afterwards, they'll be able to use only your new key. Alternatively, if you've uploaded your keys to a keyserver, tell them to refresh their keyring from Enigmail Key Management: they have to select your public key and choose Keyserver -> Refresh selected public keys (or Refresh all public keys to refresh all keys in the keyring).
Enigmail should show you revoked keys as well. If it doesn't, open Enigmail Key Management, go to View and make sure Display invalid keys is ticked.