Thunderbird 52.0

New:
Folder pane toolbar and folder view selector (replacement for folder view arrows).
Optionally remove corresponding data files when removing an account from Thunderbird.
Import settings from Becky! Internet Mail.
Possibility to copy message filter.
Dictionary setting is restored when editing a draft. Content-Language header (RFC 3282) transmitted with message.
Calendar: Event can now be created and edited in a tab.
Calendar: Processing of received invitation counter proposals.
Chat: Support Twitter Direct Messages.
Chat: Liking and favoriting in Twitter.
Chat: XMPP: Support SASL SCRAM authentication mechanism.
Chat: Support Jabber/XMPP Message Carbons (XEP-280).
Changed:
IMPORTANT: The way images are included in a compose window has changed. Images are now included as data URIs and not as references to parts of other messages or operating system files. This allows better interoperability with office packages such as MS Office or LibreOffice. Images linked from locations on the internet will no longer be downloaded and attached to the message automatically. This can be changed for each image individually via the Image Properties dialog or globally by setting the preference.
mail.compose.attach_http_images.
Correspondents column now default for all new folders, can be switched off with preference mail.threadpane.use_correspondents.
When replying to a mailing list, reply will be sent to address in From header ignoring Reply-to header.
On Linux PulseAudio is now required to play sound.
Formatting toolbar is now left in place when delivery format is switched to plain text only.
Messages in IMAP folders read on external device are now filtered by default.
Folders backed by mbox storage larger than 4GB are supported without warning (unless preference mailnews.allowMboxOver4GB is set to false).
IMAP caching now uses Mozilla's latest caching technology.
Chat: Removed Yahoo! Messenger support (since Yahoo removed support).
Fixed:
Message preview pane non-functional after IMAP folder was renamed or moved.
Editing in paragraph format: Pressing Shift+Enter sometimes doesn't move the cursor to the next line.
Various corrections when composing messages in paragraph format.
Paste as quotation doesn't always work.
Long lines in plain text replies not properly wrapped.
Undesired white-space before signature in paragraph mode.
When attachment unavailable, compose shows endless "Attaching..." message instead of error.
Text encoding of reply sometimes incorrect (uses encoding of last viewed message).
Text encoding of message display, reply or forwarded message sometimes incorrect (uses encoding of attachment).
Delivery Format not preserved for saved drafts (Auto-Detect|Plaintext|HTML|Both).
Reply to own e-mail does not reply with the correct identity.
IMAP message part caching.
Links with escaped non-ASCII (international) characters can't be clicked.
Calendar: Events specified in timezone "local time" generate alerts in UTC time.
Chat: XMPP Resource collisions.