Firefox browser can not open the Whatsapp click to chat link correctly, like Google Chrome does. The link should also be able to open without installation "https://api.whatsapp.com" like this see screenshot (1.) Firefox open error page: >The address was not understood >One of the following (whatsapp) is not registered protocol or is not allowed to use this way. >Opening an address may require a new program to be installed. Official guidelines whatsapp page: https://faq.whatsapp.com/en/android/26000030/?category=5245251 This would be a fix up to date.. Thanks!