Instead of a complicated script, your command would literally just be "firefox", or "emby". You might need to search for what the command for a given program is.
It's nowhere near as simple as it should be, but it is certainly possible.
But the cost of that would far exceed anything remotely reasonable. I say fuck it, let the birthrate drop for a few decades. The planet could use the break.
Ignore me if you're not still looking for solutions.
IIRC, some distros have a way to do this through the gui, some don't. I'm on LMDE, and it thankfully does have a gui to set startup programs.
But all distros should be able to do this. Here are some a common ways:
https://operavps.com/docs/run-command-after-boot-in-linux/
Instead of a complicated script, your command would literally just be "firefox", or "emby". You might need to search for what the command for a given program is.
It's nowhere near as simple as it should be, but it is certainly possible.