Who or what is Firefox???

Firefox is a web browser, you could compare it with Microsoft Edge or Google Chrome. More info here: https://www.mozilla.org/firefox/new/

Looks like you are using Microsoft Edge and might have ended up here by mistake?

Generally speaking, to send email in your web browser, the first step is to load up your email site, which could be Outlook, Gmail, Yahoo, or something else. You can create a bookmark for the page once you have loaded it, which will give you quicker access in the future.

I notice that the question is tagged with Sync. Do you have a problem with connecting to Sync?

• https://support.mozilla.org/en-US/kb/forum-response-firefox-sync-verification-email-faq