Rated 5 out of 5 stars

Excellent upgrade!
2 questions:
is it now required for everyone who send me encrypted messages to digitally signed their message so I can decrypt their message?

when i send an encrypted file, the recipients can decrypt the message and can't decrypt the file as it is said that the file isn't legit. What did i do wrong?

This review is for a previous version of the add-on (2.2.4). 

It's technically not required to sign an encrypted message. But doing so is mostly a good idea.

For decryption of the file, that's impossible to tell, and this is not a support forum. Please address your question at https://support.mozilla.org/products/thunderbird