Not really that worried but rather curious about your opinions. Use what suits your demands best.
But for starters:
Electron is a framework based on Chromium used to develop desktop apps. Examples of apps that are built on Electron are Discord, Element Desktop, MS Teams, Slack, GitHub Desktop, Atom, VS Code and counting
What do you mean? Is there a plugin for that?
I don’t think Firefox’s browser engine supports anything like that currently.
Yes, there’s a plethora of plugins. Most of them do need a backend executable installed to be working tho.
https://github.com/filips123/PWAsForFirefox