diff --git a/extensions/metrics/src/nsMetricsConfig.cpp b/extensions/metrics/src/nsMetricsConfig.cpp
index 45928c8ad902..550865a224c2 100644
--- a/extensions/metrics/src/nsMetricsConfig.cpp
+++ b/extensions/metrics/src/nsMetricsConfig.cpp
@@ -75,7 +75,16 @@ ReadIntegerAttr(nsIDOMElement *elem, const nsAString &attrName, PRInt32 *result)
 
 nsMetricsConfig::nsMetricsConfig()
 {
+}
+
+PRBool
+nsMetricsConfig::Init()
+{
+  if (!mEventSet.Init()) {
+    return PR_FALSE;
+  }
   Reset();
+  return PR_TRUE;
 }
 
 void
@@ -83,6 +92,8 @@ nsMetricsConfig::Reset()
 {
   // By default, we have no event limit, but all collectors are disabled
   // until we're told by the server to enable them.
+  NS_ASSERTION(mEventSet.IsInitialized(), "nsMetricsConfig::Init not called");
+
   mEventSet.Clear();
   mEventLimit = PR_INT32_MAX;
   mUploadInterval = NS_DEFAULT_UPLOAD_INTERVAL;
@@ -105,6 +116,8 @@ nsMetricsConfig::Load(nsIFile *file)
   //   <upload interval="600"/>
   // </config>
 
+  NS_ASSERTION(mEventSet.IsInitialized(), "nsMetricsConfig::Init not called");
+
   PRInt64 fileSize;
   nsresult rv = file->GetFileSize(&fileSize);
   NS_ENSURE_SUCCESS(rv, rv);
@@ -213,5 +226,6 @@ PRBool
 nsMetricsConfig::IsEventEnabled(const nsAString &eventNS,
                                 const nsAString &eventName) const
 {
+  NS_ASSERTION(mEventSet.IsInitialized(), "nsMetricsConfig::Init not called");
   return mEventSet.GetEntry(MakeKey(eventNS, eventName)) != nsnull;
 }
diff --git a/extensions/metrics/src/nsMetricsConfig.h b/extensions/metrics/src/nsMetricsConfig.h
index 4e1a1bef33f8..a939619f3981 100644
--- a/extensions/metrics/src/nsMetricsConfig.h
+++ b/extensions/metrics/src/nsMetricsConfig.h
@@ -53,9 +53,7 @@ public:
   /**
    * This method must be called before using an instance of this class.
    */
-  PRBool Init() {
-    return mEventSet.Init();
-  }
+  PRBool Init();
 
   /**
    * Restore the default configuration.
@@ -77,14 +75,18 @@ public:
   /**
    * Get the limit on the number of events that should be collected.
    */
-  PRInt32 EventLimit() {
+  PRInt32 EventLimit() const {
+    NS_ASSERTION(mEventSet.IsInitialized(),
+                 "nsMetricsConfig::Init not called");
     return mEventLimit;
   }
 
   /**
    * Get the upload interval (measured in seconds).
    */
-  PRInt32 UploadInterval() {
+  PRInt32 UploadInterval() const {
+    NS_ASSERTION(mEventSet.IsInitialized(),
+                 "nsMetricsConfig::Init not called");
     return mUploadInterval;
   }
 
@@ -92,6 +94,8 @@ public:
    * Set the upload interval (measured in seconds).
    */
   void SetUploadInterval(PRInt32 uploadInterval) {
+    NS_ASSERTION(mEventSet.IsInitialized(),
+                 "nsMetricsConfig::Init not called");
     mUploadInterval = uploadInterval;
   }