FileLink provider WeTransfer to upload large attachments.
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.
More search engines: Google and DuckDuckGo available by default in some locales.
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.
Thunderbird now compatible with other WebExtension-based FileLink add-ons like the Dropbox add-on.
Crash when using custom sound for new email notification.
Various security fixes.
Due to changes in the Mozilla platform profiles stored on Windows network shares addressed via drive letters are now addressed via UNC.
CalDav access to some servers not working. Workaround: Set preference network.cookie.same-site.enabled to false.
Chat: Twitter not working due to API changes at Twitter.com