diff --git a/browser/components/nsBrowserGlue.js b/browser/components/nsBrowserGlue.js
index 76c3cdd17391..0a3cf4463132 100644
--- a/browser/components/nsBrowserGlue.js
+++ b/browser/components/nsBrowserGlue.js
@@ -16,6 +16,9 @@ Cu.import("resource://gre/modules/AsyncPrefs.jsm");
 
 XPCOMUtils.defineLazyServiceGetter(this, "WindowsUIUtils", "@mozilla.org/windows-ui-utils;1", "nsIWindowsUIUtils");
 XPCOMUtils.defineLazyServiceGetter(this, "AlertsService", "@mozilla.org/alerts-service;1", "nsIAlertsService");
+XPCOMUtils.defineLazyGetter(this, "WeaveService", () =>
+  Cc["@mozilla.org/weave/service;1"].getService().wrappedJSObject
+);
 
 // lazy module getters
 
@@ -973,6 +976,10 @@ BrowserGlue.prototype = {
 
     AutoCompletePopup.init();
     DateTimePickerHelper.init();
+    // Check if Sync is configured
+    if (Services.prefs.prefHasUserValue("services.sync.username")) {
+      WeaveService.init();
+    }
 
     this._firstWindowTelemetry(aWindow);
     this._firstWindowLoaded();
diff --git a/services/sync/SyncComponents.manifest b/services/sync/SyncComponents.manifest
index 6493bb2242ef..faeafd8b6d4b 100644
--- a/services/sync/SyncComponents.manifest
+++ b/services/sync/SyncComponents.manifest
@@ -1,18 +1,6 @@
-# WeaveService has to restrict its registration for the app-startup category
-# to the specific list of apps that use it so it doesn't get loaded in xpcshell.
-# Thus we restrict it to these apps:
-#
-#   b2g:            {3c2e2abc-06d4-11e1-ac3b-374f68613e61}
-#   browser:        {ec8030f7-c20a-464f-9b0e-13a3a9e97384}
-#   mobile/android: {aa3c5121-dab2-40e2-81ca-7ea25febc110}
-#   mobile/xul:     {a23983c0-fd0e-11dc-95ff-0800200c9a66}
-#   suite (comm):   {92650c4d-4b8e-4d2a-b7eb-24ecf4f6b63a}
-#   graphene:       {d1bfe7d9-c01e-4237-998b-7b5f960a4314}
-
 # Weave.js
 component {74b89fb0-f200-4ae8-a3ec-dd164117f6de} Weave.js
 contract @mozilla.org/weave/service;1 {74b89fb0-f200-4ae8-a3ec-dd164117f6de}
-category app-startup WeaveService service,@mozilla.org/weave/service;1 application={3c2e2abc-06d4-11e1-ac3b-374f68613e61} application={ec8030f7-c20a-464f-9b0e-13a3a9e97384} application={aa3c5121-dab2-40e2-81ca-7ea25febc110} application={a23983c0-fd0e-11dc-95ff-0800200c9a66} application={92650c4d-4b8e-4d2a-b7eb-24ecf4f6b63a} application={99bceaaa-e3c6-48c1-b981-ef9b46b67d60} application={d1bfe7d9-c01e-4237-998b-7b5f960a4314}
 component {d28f8a0b-95da-48f4-b712-caf37097be41} Weave.js
 contract @mozilla.org/network/protocol/about;1?what=sync-log {d28f8a0b-95da-48f4-b712-caf37097be41}
 
diff --git a/services/sync/Weave.js b/services/sync/Weave.js
index 2375ccc587a9..966e94888124 100644
--- a/services/sync/Weave.js
+++ b/services/sync/Weave.js
@@ -94,6 +94,32 @@ WeaveService.prototype = {
     return onReadyPromise;
   },
 
+  init() {
+    // Force Weave service to load if it hasn't triggered from overlays
+    this.timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
+    this.timer.initWithCallback({
+      notify: () => {
+        let isConfigured = false;
+        // We only load more if it looks like Sync is configured.
+        if (this.enabled) {
+          // We have an associated FxAccount. So, do a more thorough check.
+          // This will import a number of modules and thus increase memory
+          // accordingly. We could potentially copy code performed by
+          // this check into this file if our above code is yielding too
+          // many false positives.
+          Components.utils.import("resource://services-sync/main.js");
+          isConfigured = Weave.Status.checkSetup() != Weave.CLIENT_NOT_CONFIGURED;
+        }
+        let getHistogramById = Services.telemetry.getHistogramById;
+        getHistogramById("WEAVE_CONFIGURED").add(isConfigured);
+        if (isConfigured) {
+          getHistogramById("WEAVE_CONFIGURED_MASTER_PASSWORD").add(Utils.mpEnabled());
+          this.ensureLoaded();
+        }
+      }
+    }, 10000, Ci.nsITimer.TYPE_ONE_SHOT);
+  },
+
   /**
    * Whether Sync appears to be enabled.
    *
@@ -105,42 +131,6 @@ WeaveService.prototype = {
   get enabled() {
     let prefs = Services.prefs.getBranch(SYNC_PREFS_BRANCH);
     return prefs.prefHasUserValue("username");
-  },
-
-  observe(subject, topic, data) {
-    switch (topic) {
-    case "app-startup":
-      let os = Cc["@mozilla.org/observer-service;1"].
-               getService(Ci.nsIObserverService);
-      os.addObserver(this, "final-ui-startup", true);
-      break;
-
-    case "final-ui-startup":
-      // Force Weave service to load if it hasn't triggered from overlays
-      this.timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
-      this.timer.initWithCallback({
-        notify: () => {
-          let isConfigured = false;
-          // We only load more if it looks like Sync is configured.
-          if (this.enabled) {
-            // We have an associated FxAccount. So, do a more thorough check.
-            // This will import a number of modules and thus increase memory
-            // accordingly. We could potentially copy code performed by
-            // this check into this file if our above code is yielding too
-            // many false positives.
-            Components.utils.import("resource://services-sync/main.js");
-            isConfigured = Weave.Status.checkSetup() != Weave.CLIENT_NOT_CONFIGURED;
-          }
-          let getHistogramById = Services.telemetry.getHistogramById;
-          getHistogramById("WEAVE_CONFIGURED").add(isConfigured);
-          if (isConfigured) {
-            getHistogramById("WEAVE_CONFIGURED_MASTER_PASSWORD").add(Utils.mpEnabled());
-            this.ensureLoaded();
-          }
-        }
-      }, 10000, Ci.nsITimer.TYPE_ONE_SHOT);
-      break;
-    }
   }
 };