Favicon is an icon that is shown in the browser address bar or tab when viewing your project. You can upload a favicon to your profile to display across all of your projects or create specific graphics for each of them.
A favicon can only be added to projects or profiles with a custom domain. You can use any static image as a favicon, but please keep in mind that it’s better to use images no bigger than 256x256px.
Set to a project. Open the project settings and click the Domain tab. Map a custom domain. After that, the favicon can be uploaded.
Set to the profile page. Open your profile settings and find the Public Profile section. Map a custom domain. After that, the favicon can be uploaded.
Learn more about public profiles here.