Email links in web pages no longer opening Xfinity email Mac OS, Firefox browser

I used to be able to click on email addresses in a web page, and the list of options contained Xfinity email as one of the ways to open the address. This would open an Xfinity email web page to compose an email to that mail address.

This no longer happens, Gamil and Yahoo mail are stil llisted as valid options. Have tried turning popup blocker offand deleting all cookies, with no success.

Browser: Firefox 69.0.3 (64-bit)

OS: MacOS Sierra 10.12.6