The last weeks demonstrate how personal information are sensitive and valuable. Companies like Ebay, Spotify, AVAST have been hacked and stolen of their client databases. Those facts motivate me to host my own Firefox Sync server instead of uploading my data to another big cloud company.
Firefox Sync is a solution to store and keep synchronize Firefox data like bookmarks, history, passwords or preferences. Since Firefox 29, a new version of Sync is available (version 1.5). It uses the new Firefox accounts as authentication mechanism. The service definition and separation between authentication, token and storage allow to change and plug new servers on the fly. So you could host your own Sync server without having to worry about auth. Auth will be provided by Mozilla servers, which don’t store your plain text passwords or encryption keys. You may check the source code of the authentication server on Github or the Sync protocol for more details.
The Sync server installation procedure is quite well described by Mozilla. It explains how to get, build and run and test a custom Sync server on the built-in server (some git and make commands). Once everything works, you could set up your Firefox browser to point at your own server and test with your account and data. For production use, you could bind it on your Apache on Ngnix server throw WSGI or Gunicorn module (the built-in server is not intended to be use in production context).
In conclusion, I run my own Sync server to store my personal data. The server is lightweight and data takes less than 10 mo of storage. I enforced the security with requested client certificate and IP filtering and I could have a look to all access done with the Apache logs. So even if Firefox accounts are leaked (and we should consider they will be), attacker needs to know location of the server, get a certificate, find a valid IP address before getting access to my Sync server. According the interest of my data, the risk is very low.
I encourage your to host as often as possible your data. Nowadays, it is the real people value. So take care of it and thanks the Mozilla company to allow us to do it (hey Google, what about Chrome ?).