What do you mean? Just install the plug-in PWAs for Firefox. I have a Firefox based WhatsApp PWA that runs separate from my main Firefox process. It launches on its own and uses the WhatsApp icon on the taskbar. (I was having so many issues with the official WhatsApp app).

It does have a dependency on a package you’ll have to install outside of FF but you can install it using Chocolatey so it’s pretty quick and easy.