Yes, of course. Although I can't vouch for its security and stability - while I use it myself and it seems to work OK, I'd rather state that it's risky. In short, the repo is more like a code dump, rather than a properly released project.
Still, here it is: https://gitlab.com/drdaeman/firesync
Development is very sporadic, though - you can see it in commit history. And some parts of code feel dirty (in particular, I've made a bad design decision when trying to avoid implementing full-fledged OAuth2).
The repo lacks few things:
1) Notes about patched PyBrowserID. It's in the repo, and you can check the Dockerfile, but not in README.
2) Instructions on installing Kinto - another piece that is used to sync WebExtension settings[1]. It became mandatory with 57, without it sync fails and doesn't update "last synced" date (used to work in 56 and below). I'll add some instructions later, when I'll find time to do so.
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[1] BTW, this means that everyone who runs self-hosted Sync but not Accounts (relying on Mozilla tokens instead) are now storing parts of their data on Mozilla servers. I don't think this was ever announced, I've only learned about Kinto when my Firefoxes started to log errors in the browser console. If you self-host Sync-only and think you may be affected - check `webextensions.storage.sync.serverURL` value.
