Thunderbird 136.0 (64-bit)

What's new in this version:

New:
- Messages are automatically adapted to dark mode with a quick toggle in the header
- New "Appearance" Settings UI to globally control message threading/sorting order

Changed:
- Criteria for closing idle message databases

Fixed:
- Thunderbird Release channel was not displayed in "About Thunderbird"
- Crash could occur when shutting down during MAPI send
- The error message for compacting a corrupted local folder was not useful
- Deleting or detaching attachments in a saved .eml file appeared to work but failed
- On HiDPI screens, clicking addresses in the header could show popup off-screen
- Opening an .EML file in profiles with many folders could take a long time
- Some messages may have been threaded incorrectly in unified folders
- Unified folders could become unusable instead of being automatically rebuilt
- Folders at level 3+ were not auto-discovered when IMAP subscriptions were ignored
- New subfolder did not inherit parent view, sort order, sort type, or columns
- With "Fetch headers only" enabled, messages could not be sorted by size
- Selecting starred messages did not update immediately
- Marking a unified folder as favorite did not show it in favorite folders
- Users with many folders experienced poor performance when resizing message panes
- The UI could falsely report a message as encrypted when a null cipher was used
- Search messages dialog list could not be sorted by clicking the header icon
- Sending to multiple SMTPs could fail silently due to missing address book
- "Replace" button in compose window was overwritten when the window was narrow
- Changing the UI font size did not apply to some dialogs
- Deleted Gmail messages stayed visible until compact/expunge, despite settings
- Export to mobile did not work when "Use default server" was selected
- Account settings menu could be loaded twice
- Account Settings updated font size were not reflected in the content frame
- Add-ons: Context menu entries were incorrectly aligned
- Middle-click autoscroll cursor appeared without arrows instead of expected design
- Some functionality was missing for newsgroup messages opened from a file or URI
- Notifications for new mail were not showing for IMAP
- Message and folder lists could display incorrect line spacing after restart
- Clicking a 'mid:' link could clear the thread pane and cause errors
- Release channel incorrectly showed What's New page after update
- "Save Link As" was not working in feed web content
- Sort indicators were missing on the calendar events list
- Visual and UX improvements
- Security fixes