https://addons.mozilla.org/en-US/firefox/addon/addfox/

address book for your online life! Save and manage contacts with emails, addresses, and phone numbers

To test, go to about:debugging#/runtime/this-firefox, select "Load Temporary Add-on," and upload this as a ZIP file.

This is a semi-beta add-on. Feel free to do whatever you want with it, but I am not responsible for any actions taken using it (yes, it's open source LOL).

I'm not a programmer and just made this for myself, but if someone else finds it useful, feel free to try it out.