... for historical reasons, here the text for the outdated Addon:
Thunderbird/Lightning extension for showing the calender week in the month/multiweek view.
If installed, the calender week will be displayed in the first day of the week (in the calendar's month and multiweek view)
This Add-on was inspired by the Calendar Tweaks Add-on.
Source code available on GitHub/thunderbird-addon-show-cw.