Hi bug1,
I appreciate your detailed explanation, as it helps us understand the problem better. It seems like you've encountered a specific bug that could be related to browser compatibility or certain plugins in use. While I'm glad to hear that it works as expected in Chrome, I understand the importance of resolving this issue in your preferred browser.
You can temporarily disable your plugins, particularly NoScript, to see if they are causing any interference with the date selection feature. You can also try to clear your browser cache and cookies, as this can sometimes resolve unexpected behavior. Lastly, ensure that your Firefox-ESR is up to date.
Regards,
Sai