--- a/dom/alarm/AlarmService.jsm
+++ b/dom/alarm/AlarmService.jsm
@@ -42,17 +42,17 @@ let AlarmService = {
 
     // add the messages to be listened
     const messages = ["AlarmsManager:GetAll", "AlarmsManager:Add", "AlarmsManager:Remove"];
     messages.forEach(function addMessage(msgName) {
         ppmm.addMessageListener(msgName, this);
     }.bind(this));
 
     // set the indexeddb database
-    let idbManager = Components.classes["@mozilla.org/dom/indexeddb/manager;1"].getService(Ci.nsIIndexedDatabaseManager);
+    let idbManager = Cc["@mozilla.org/dom/indexeddb/manager;1"].getService(Ci.nsIIndexedDatabaseManager);
     idbManager.initWindowless(myGlobal);
     this._db = new AlarmDB(myGlobal);
     this._db.init(myGlobal);
 
     // variable to save alarms waiting to be set
     this._alarmQueue = [];
 
     this._restoreAlarmsFromDb();
@@ -95,30 +95,30 @@ let AlarmService = {
         let newAlarm = {
           date: json.date, 
           ignoreTimezone: json.ignoreTimezone, 
           timezoneOffset: this._currentTimezoneOffset, 
           data: json.data,
           manifestURL: json.manifestURL
         };
 
+        let newAlarmTime = this._getAlarmTime(newAlarm);
+        if (newAlarmTime <= Date.now()) {
+          debug("Adding a alarm that has past time. Return DOMError.");
+          this._debugCurrentAlarm();
+          this._sendAsyncMessage(mm, "Add", false, json.requestId, "InvalidStateError");
+          break;
+        }
+
         this._db.add(
           newAlarm,
           function addSuccessCb(aNewId) {
             debug("Callback after adding alarm in database.");
 
             newAlarm['id'] = aNewId;
-            let newAlarmTime = this._getAlarmTime(newAlarm);
-
-            if (newAlarmTime <= Date.now()) {
-              debug("Adding a alarm that has past time. Don't set it in system.");
-              this._debugCurrentAlarm();
-              this._sendAsyncMessage(mm, "Add", true, json.requestId, aNewId);
-              return;
-            }
 
             // if there is no alarm being set in system, set the new alarm
             if (this._currentAlarm == null) {
               this._currentAlarm = newAlarm;
               this._debugCurrentAlarm();
               this._sendAsyncMessage(mm, "Add", true, json.requestId, aNewId);
               return;
             }
@@ -143,17 +143,17 @@ let AlarmService = {
           }.bind(this),
           function addErrorCb(aErrorMsg) {
             this._sendAsyncMessage(mm, "Add", false, json.requestId, aErrorMsg);
           }.bind(this)
         );
         break;
 
       case "AlarmsManager:Remove":
-        this._db.remove(
+        this._removeAlarmFromDb(
           json.id,
           function removeSuccessCb() {
             debug("Callback after removing alarm from database.");
 
             // if there is no alarm being set
             if (!this._currentAlarm) {
               this._debugCurrentAlarm();
               return;
@@ -178,20 +178,17 @@ let AlarmService = {
               this._currentAlarm = alarmQueue.shift();
               this._debugCurrentAlarm();
               return;
             }
 
             // no alarm waiting to be set in the queue
             this._currentAlarm = null;
             this._debugCurrentAlarm();
-          }.bind(this),
-          function removeErrorCb(aErrorMsg) {
-            throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
-          }
+          }.bind(this)
         );
         break;
 
       default:
         throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
         break;
     }
   },
@@ -222,39 +219,62 @@ let AlarmService = {
       default:
         throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
         break;
     }
 
     aMessageManager.sendAsyncMessage("AlarmsManager:" + aMessageName + ":Return:" + (aSuccess ? "OK" : "KO"), json);
   },
 
+  _removeAlarmFromDb: function _removeAlarmFromDb(aId, aRemoveSuccessCb) {
+    debug("_removeAlarmFromDb()");
+
+    // If the aRemoveSuccessCb is undefined or null, set a 
+    // dummy callback for it which is needed for _db.remove()
+    if (!aRemoveSuccessCb) {
+      aRemoveSuccessCb = function removeSuccessCb() {
+        debug("Remove alarm from DB successfully.");
+      };
+    }
+
+    this._db.remove(
+      aId,
+      aRemoveSuccessCb,
+      function removeErrorCb(aErrorMsg) {
+        throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
+      }
+    );
+  },
+
+  _fireSystemMessage: function _fireSystemMessage(aAlarm) {
+    debug("Fire system message: " + JSON.stringify(aAlarm));
+    let manifestURI = Services.io.newURI(aAlarm.manifestURL, null, null);
+    messenger.sendMessage("alarm", aAlarm, manifestURI);
+  },
+
   _onAlarmFired: function _onAlarmFired() {
     debug("_onAlarmFired()");
 
     if (this._currentAlarm) {
-      debug("Fire system intent: " + JSON.stringify(this._currentAlarm));
-      let manifestURI = Services.io.newURI(this._currentAlarm.manifestURL, null, null);
-      messenger.sendMessage("alarm", this._currentAlarm, manifestURI);
+      this._fireSystemMessage(this._currentAlarm);
+      this._removeAlarmFromDb(this._currentAlarm.id);
       this._currentAlarm = null;
     }
 
-    // reset the next alarm from the queue
-    let nowTime = Date.now();
+    // Reset the next alarm from the queue.
     let alarmQueue = this._alarmQueue;
     while (alarmQueue.length > 0) {
       let nextAlarm = alarmQueue.shift();
       let nextAlarmTime = this._getAlarmTime(nextAlarm);
 
-      // if the next alarm has been expired, directly 
-      // fire system intent for it instead of setting it
-      if (nextAlarmTime <= nowTime) {
-        debug("Fire system intent: " + JSON.stringify(nextAlarm));
-        let manifestURI = Services.io.newURI(nextAlarm.manifestURL, null, null);
-        messenger.sendMessage("alarm", nextAlarm, manifestURI);
+      // If the next alarm has been expired, directly 
+      // fire system message for it instead of setting it.
+      if (nextAlarmTime <= Date.now()) {
+        this._fireSystemMessage(nextAlarm);
+        this._removeAlarmFromDb(nextAlarm.id);
       } else {
         this._currentAlarm = nextAlarm;
         break;
       }
     }
     this._debugCurrentAlarm();
   },