Epichrome is a fantastic solution for site-specific browsers (AKA SSBs). Yet, I prefer Firefox to Chrome due to its great extensibility. Also, even though Epichrome is great, it has problems like copying extensions for an SSB from one workstation to another. Firefox has no such problems; you can seamlessly copy settings, extensions, and everything from one machine to another since everything is neatly stored in a single profile folder.
According to Mozilla Wiki, there used to be a project called Prism which was an SSB for Firefox. It sounds quite nice, similar to Epichrome, and geared towards Firefox. Sadly, Mozilla dropped the project and the links which point to its alleged successor are all dead. So it seems that Prism is just dead. Is there anything like Prism for our modern day and age? I would prefer something that is free (i.e., gratis) and open-source would be nice, too.