how to make it default

firefox.com is a website while Firefox is a web browser you can use to view the firefox.com site. How to make Firefox as the default web browser on Android see https://support.mozilla.org/en-US/kb/make-firefox-default-browser-android Or if you are referring to search engines in Firefox then see https://support.mozilla.org/en-US/kb/manage-my-default-search-engines-firefox-android