diff --git a/extensions/firefox/content/PdfStreamConverter.jsm b/extensions/firefox/content/PdfStreamConverter.jsm
index 9e455a7f6..28ec7e156 100644
--- a/extensions/firefox/content/PdfStreamConverter.jsm
+++ b/extensions/firefox/content/PdfStreamConverter.jsm
@@ -452,7 +452,7 @@ ChromeActions.prototype = {
     getChromeWindow(this.domWindow).gFindBar
                                    .updateControlState(result, findPrevious);
   },
-  setPreferences: function(prefs) {
+  setPreferences: function(prefs, sendResponse) {
     var defaultBranch = Services.prefs.getDefaultBranch(PREF_PREFIX + '.');
     var numberOfPrefs = 0;
     var prefValue, prefName;
@@ -483,8 +483,11 @@ ChromeActions.prototype = {
           break;
       }
     }
+    if (sendResponse) {
+      sendResponse(true);
+    }
   },
-  getPreferences: function(prefs) {
+  getPreferences: function(prefs, sendResponse) {
     var defaultBranch = Services.prefs.getDefaultBranch(PREF_PREFIX + '.');
     var currentPrefs = {}, numberOfPrefs = 0;
     var prefValue, prefName;
@@ -510,7 +513,11 @@ ChromeActions.prototype = {
           break;
       }
     }
-    return JSON.stringify(currentPrefs);
+    if (sendResponse) {
+      sendResponse(JSON.stringify(currentPrefs));
+    } else {
+      return JSON.stringify(currentPrefs);
+    }
   }
 };
 
diff --git a/web/firefoxcom.js b/web/firefoxcom.js
index 3e1b9b2cc..8ccb87570 100644
--- a/web/firefoxcom.js
+++ b/web/firefoxcom.js
@@ -106,15 +106,15 @@ var DownloadManager = (function DownloadManagerClosure() {
 
 Preferences._writeToStorage = function (prefObj) {
   return new Promise(function (resolve) {
-    FirefoxCom.requestSync('setPreferences', prefObj);
-    resolve();
+    FirefoxCom.request('setPreferences', prefObj, resolve);
   });
 };
 
 Preferences._readFromStorage = function (prefObj) {
   return new Promise(function (resolve) {
-    var readPrefs = JSON.parse(FirefoxCom.requestSync('getPreferences',
-                                                      prefObj));
-    resolve(readPrefs);
+    FirefoxCom.request('getPreferences', prefObj, function (prefStr) {
+      var readPrefs = JSON.parse(prefStr);
+      resolve(readPrefs);
+    });
   });
 };