compton2059 said

I can't find a mail merge add on that is compatible with Quantum. Can anyone suggest one?

Assuming you're using Thunderbird, would you give this add-on a try  ?

https://addons.mozilla.org/en-US/thunderbird/addon/mail-merge/

Yes.. I should have been clear I am using Thunderbird.

This link downloads a .xpi file. Quantum is not compatible with .xpi as far as I can tell. It will not install.

Firefox will not transfer the file over to Thunderbird to install if that is what you were expecting.

https://support.mozilla.org/en-US/kb/thunderbird-add-ons-frequently-asked-questions#w_where-do-i-get-add-ons

compton2059 said

Yes.. I should have been clear I am using Thunderbird. This link downloads a .xpi file. Quantum is not compatible with .xpi as far as I can tell. It will not install.

Please see :

https://support.mozilla.org/en-US/kb/installing-addon-thunderbird

(you'll have to scroll down some)