Comment 28 for bug 643899

I think the root cause for this is:

toolkit/modules/Preferences.jsm:

  _get: function(prefName, defaultValue) {
    switch (this._prefSvc.getPrefType(prefName)) {
      case Ci.nsIPrefBranch.PREF_STRING:
        return this._prefSvc.getComplexValue(prefName, Ci.nsISupportsString).data;

In the case of localizable prefs, that should be gCV(prefName, Ci.nsIPrefLocalizedString) to get the right value. I think the code as written will grab intl.properties instead of actually reading the real value.

But even that might be broken -- when syncing between two Firefoxes with different locales.

I suspect there needs to be more sophisticated handling here altogether.