How do I integrate add to home screen into PWA?
Open the menu next to the URL bar. Depending on whether you're using Chrome or Android you'll see a menu option "Install" or "Install App". This is the "Add to Home screen" option displayed for any site that has the necessary features in place.
Does Firefox support progressive web apps?
Although Firefox supports many of Progressive Web App APIs, it does not support functionality to install them as a standalone system app with an app-like experience.