Issue 2850 - Get rid of synchronous XMLHttpRequest on startup, embed JSON files directly instead

lib/prefs.js

Index: lib/prefs.js
===================================================================
--- a/lib/prefs.js
+++ b/lib/prefs.js
@@ -12,23 +12,19 @@ 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 request = new XMLHttpRequest();
-  request.open("GET", addonRoot + "defaults/prefs.json", false);
-  request.responseType = "json";
-  request.send();
-
-  let defaults = request.response.defaults;
-  let preconfigurable = new Set(request.response.preconfigurable);
+  let prefsData = require("prefs.json");
+  let defaults = prefsData.defaults;
+  let preconfigurable = new Set(prefsData.preconfigurable);
   for (let pref in defaults)
   {
     let value = defaults[pref];
     let [getter, setter] = typeMap[typeof value];
     if (preconfigurable.has(pref))
     {
       try
       {