This is to report multiple issues with Thunderbird Version 91 on Fedora Linux. (I have also entered Bugzillas for these.) I upgraded from Version 78, using the standard Fedora repos. 1. Cannot Send Mail My setup defaults to include my own address in the Bcc field. When I go to create a new message, entering an address, I see the Send button is grayed out. If I delete my address from the Bcc field, the Send button appears to become active. However, attempting to send the message fails--in fact, nothing at all happens when I click the (apparently active) Send button. When replying to an e-mail, nothing I do (e.g., clearing the Bcc field) activates the Send button. And, nothing happens when I hit Send. I have tried Troubleshooting mode and results above are the same. 2. Loss of Address Book After the upgrade to version 91, my address book appears to be empty. However, entering part of an e-mail address in the To: field that I *know* is in the address book auto-completes. Thus, it would appear the application has some access to the data in the address book, even though I cannot see it. (Due to these issues, I have downgraded to Version 78; address book is completely gone now. Presumably, Version 91 did some conversion that isn't reversible in a downgrade.) 3. Loss of "movemail" mailbox. Local system mailspool no longer visible as "movemail." This can be re-enabled in Edit->Account Settings->Account Actions.