Calendar: Default values for the first day of the week and working days are now derived from the selected datetime formatting locale (restart after changing locale in the OS required).
Calendar: Switch to a Photon-style icon set for all platforms.
Multiple requests for master password when Google Mail or Calendar OAuth2 is enabled.
Scrollbar of the address entry auto-complete popup does not work.
Security info dialog in compose window does not show certificate status.
Links in the Add-on Manager's search results and theme browsing tabs open in external browser.
Localized versions of Thunderbird didn't show a localized name for the "Drafts" and "Sent" folders for certain IMAP providers (particularly in France).
Replying to a message with an empty subject inserted Re: twice (not working in Thunderbird 60.0).
Spellcheck marks disappeared erroneously for words with an apostrophe (not working in Thunderbird 60.0).
Calendar: First day of the week cannot be set.
Calendar: Several fixes related to cutting/deleting of events and email scheduling.
Thunderbird will hang if HTML signature references non-existent image (solution forthcoming).
Chat: Twitter not working due to API changes at Twitter.com (solution forthcoming).