I use Firefox (LibreWolf with Mozilla sync) on multiple devices. To have my tabs, extensions and history easy available I use Mozilla for syncing that data.
Would it be possible to just use a generic sync service like rsync or something, to sync the profile folders and every file in it?
Or would that break or corrupt data?
Also can easily run a local webdav server with SFTPGo on Linux/BSD/OSX/Windows: https://docs.sftpgo.com/latest/installation/
Or use it directly with your devices to sync instead of going through syncthing.