I couldn't find this information on either Firepad documentation or CodeMirror. I have read CodeMirror is npm bundle based. Is Firepad compatible with CodeMirror 6 ?
Is Firepad compatible with CodeMirror 6 ?
Probably not. At the time of writing, Firepad is running on 5.52.2 (see package.json) and isn't actively developed anymore (see README.md):
This repository is no longer under active development. No new features will be added and issues are not actively triaged. Pull Requests which fix bugs are welcome and will be reviewed on a best-effort basis.
Since Codemirror 6 seems a complete rewrite with a new architecture, I don't think anymore will bother to port it over at the moment.