Thunderbird 65.0 Beta 2 Email Client for PC Windows

What’s New:
FileLink for WeTransfer.
WebExtensions FileLink API to facilitate FileLink add-ons. WeTransfer is already included and Dropbox is available as add-on.
Various theme improvements including a dark message list/thread pane.
When multiple language packs are installed, the UI language can now be selected in the Advanced Options. Preference intl.multilingual.enabled needs to be set (and possily also extensions.langpacks.signatures.required needs to be set to false).

Changed:
ADD-ON SUPPORT: Restartless add-ons continue to work if their authors have made the necessary minor adjustments. Non-restartless legacy add-ons using XUL overlays are only supported if add-on authors have adapted them. Apart from Lightning/Calendar there are a few that have been adapted, like "ThunderHTMLedit", "Compact Header" and "Signature Switch". Instaling legacy add-ons now requires a restart. Legacy add-ons can now specify an options page again.
DICTIONARY SUPPORT: Only WebExtension dictionaries are supported now. Please download new dictionaries from addons.mozilla.org since addons.thunderbird.net still provides "legacy" dictionaries compatible with Thunderbird 60 ESR. This may change as soon as Thunderbird 60 ESR can also handle WebExtension dictionaries (planned for version 60.5).
Reply to self will now search all identities (default of preference mailnews.reply_to_self_check_all_ident changed to true).
Composition text and background colors no longer sent by default. New option in "Tools > Options, Composition".

Fixed:
Address book search and auto-complete slowness introduced in Thunderbird 64 beta.
Plain text markup with * for bold, / for italics, _ for underline and | for code did not work when the enclosed text contained non-ASCII characters.
While composing a message, a link not removed when link location was removed in the link properties panel.
Decoding problems for messages with less common charsets (cp932, cp936).
Spurious 
 (encoded newline) inserted into drafts and sent email.
Double-clicking on a word in the Write window sometimes launched the Advanced Property Editor or Link Properties dialog.
Editing a plaint text draft displayed the entire message as quote (in blue).
New messages in the drafts folder (and other special or virtual folders) will no longer be included in the new messages notification.
Edit > Undo didn't undo moving or deleting of messages.
Improvements of SMTP 5.7.1 message.

Beta 2 - New and Fixed in Thunderbird 65 beta 2:
Thunderbird now allows the addition of OpenSearch search engines from a local XML file using a minimal user inferface: [+] button to select a file an add, [-] to remove. Note: The set of search engines will be improved the next version, Google and DuckDuckGo will be available by default.
During account creation, Thunderbird will now detect servers using the Microsoft Exchange protocol. It will offer the installation of a 3rd party add-on (Owl) which supports that protocol.

Fixed:
Account creation sometimes shows an error: "Programming bug. Assertion failed, see log".
Chat: Participants not sorted (not working since Thunderbird 63 beta).

Known Issues
Unresolved:
Due to changes in the Mozilla platform profiles stored on Windows network shares addressed via drive letters are now addressed via UNC.
Spellcheck marks disappeared erroneously for words with an apostrophe (working in Thunderbird ESR.
Calendar: A localized version of Provider for Google Calendar not available at addons.thunderbird.net or the Mozilla FTP server. A US-English version can be downloaded here.
Chat: Twitter not working due to API changes at Twitter.com