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Join UsVersion 74.0beta, first offered to channel users on February 17, 2020
MailExtensions: API to block sending a message from compose window
MailExtensions: API to interact with message in compose window
Add-on support: As of version 74.0 beta, Thunderbird only supports MailExtensions and MailExtension Experiments. Restartless add-ons and non-restartless legacy add-ons using XUL overlays are no longer supported.
Calendar: The Lightning calendar add-on is now integrated into Thunderbird
Account Manager moved to a tab
Improved UI of global search results tab
MailExtensions: Allow commands.update() to disable a command
MailExtensions: Allow browser.query.messages to query by tag
MailExtensions: Changed folder enumeration to return tree structure rather than list
MailExtensions: Exposed message "Junk" status to addons
When copying messages from an IMAP folder to a local folder, offline store wasn't used
SMTP timeout when forwarding message via filter
Partial updates not working
Thread collapsed when opening news message in a new window
Addons not automatically updated to compatible version after upgrade from Thunderbird 60
Opening the properties of a folder sometimes hung on Mac
Multiple master password prompts. Fixed by prompting for master password at startup time.
Offline replication of LDAP databases sometimes failed to replace an earlier copy
Calendar: Last day of multiple-day event not displayed
Chat: Avatars not displayed in tooltips
Thunderbird will now display a popup window when starting up on a new profile
MailExtensions: Action APIs now provide tab and click information
MailExtensions: Allow composeAction to open popups from onBeforeSend
Long subject lines did not wrap in message header
Account Manager in tab not consistent with Options/Preferences in tab
"Get New Messages for All Accounts" not working for OAuth2-authenticated IMAP accounts
Searching in message bodies led to false negatives under some circumstances in quoted-printable encoded HTML bodies
Calendar: Starting with 74.0 beta 2, building Thunderbird with --enable-calendar is deprecated, and should be removed from your mozconfig file
Chat: macOS users were not be able to connect to a server
WebExtension toolbar button badges not displayed
Address auto-completion not working on Mac if the Mac address book is enabled (File > Use Mac OS X Address Book)