Issue 1489 - Support preconfigured defaults

lib/prefs.js

 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 let {addonRoot, addonName} = require("info");
 let branchName = "extensions." + addonName + ".";
 let branch = Services.prefs.getBranch(branchName);
+let preconfiguredBranch =
+    Services.prefs.getBranch(branchName + "preconfigured.");
 let ignorePrefChanges = false;
 
 function init()
 {
   // Load default preferences and set up properties for them
   let defaultBranch = Services.prefs.getDefaultBranch(branchName);
   let scope =
   {
-    pref: function(pref, value)
+    pref: function(pref, value, preconfigurable)
     {
       if (pref.substr(0, branchName.length) != branchName)
       {
         Cu.reportError(new Error("Ignoring default preference " + pref + ", wrong branch."));
         return;
       }
       pref = pref.substr(branchName.length);
 
       let [getter, setter] = typeMap[typeof value];
+      if (preconfigurable)
+      {
+        try
+        {
+          value = getter(preconfiguredBranch, pref);
+        }
+        catch (e) {}
+      }
       setter(defaultBranch, pref, value);
       defineProperty(pref, false, getter, setter);
     }
   };
   Services.scriptloader.loadSubScript(addonRoot + "defaults/prefs.js", scope);
 
   // Add preference change observer
   try
   {
     branch.QueryInterface(Ci.nsIPrefBranch2).addObserver("", Prefs, true);
@@ skipping 142 matching lines @@
 {
   let str = Cc["@mozilla.org/supports-string;1"].createInstance(Ci.nsISupportsString);
   str.data = newValue;
   branch.setComplexValue(pref, Ci.nsISupportsString, str);
 }
 
 function getJSONPref(branch, pref) JSON.parse(getCharPref(branch, pref))
 function setJSONPref(branch, pref, newValue) setCharPref(branch, pref, JSON.stringify(newValue))
 
 init();