How to make Yahoo Mail the default email in Windows or your web browser?
When you select a main email "mailto" in your browser, that email program will be the one that will be opened every time you click on the "Contact Us" link. You can change your browser or Windows settings so that Yahoo Mail is the one that opens automatically.
Firefox is one of the web browsers that support Yahoo Mail as an email option. Set Yahoo Mail as your default in Firefox.
Another option is to apply the default email address at the operating system level. This allows any browser that does not have an email preference set to, select Yahoo Mail. You can set your default email in Windows 10.