I'm not sure, that can be stated as fact, but for this subtopic (How to run all FXA and syncserver selfhosted) the docs make it sound easy to deploy/run. As expected, after all, the featureset needed isn't huge for "Maintain a list of tabs per browsers per User, authenticated via some backend plugin for the syncserver". But then you read, that you need to run half a dozen "fxa-something" servers, in addition to the SyncServer. And a clear writeup of those is what I briefly check for every few months, but haven't found yet.