Change the configuration in firefox (with about:config):
services.sync.tokenServerURI: http://localhost:5000/token/1.0/sync/1.5
See the pull request to have the packages for nix.
The nix commands are:
$ nix-build ./default.nix -A pythonPackages.syncserver -o syncserver
$ nix-build ./default.nix -A pythonPackages.pasteScript -o paste
Then, start your very own shiny new server with:
$ PYTHONPATH=$(pwd)/syncserver/lib/python2.7/site-packages ./paste/bin/paster serve syncserver.ini