Mozilla Thunderbird 91.7.0のダウンロード

Changes
- Thunderbird will use the first occurrence of headers that should only appear once

Fixes
- Auto-complete incorrectly changed a pasted email address to the primary address of a contact
- Attachments with filename extensions that were not registered in MIME types could not be opened
- Copy/Cut/Paste actions not working in Thunderbird Preferences
- Improved screen reader support of displayed message headers
- Various security fixes