so in firefox, you can go to about:config and change the value of browser.ssb.enabled to true

and then when you run firefox with the -ssb flag, it opens in an SiteSpecificBrowser. or an "app window"
Image is an example of it connecting to my code-server instance. I ran D:\PortableApps\Firefox Developer Edition\firefox.exe --ssb https://code.example.com

It is a viable way, all that is needed is making it automatically set this setting to true