--- a/mobile/android/base/java/org/mozilla/gecko/BrowserApp.java
+++ b/mobile/android/base/java/org/mozilla/gecko/BrowserApp.java
@@ -1369,16 +1369,17 @@ public class BrowserApp extends GeckoApp
             }
         });
 
         for (final BrowserAppDelegate delegate : delegates) {
             delegate.onStart(this);
         }
 
         MmaDelegate.track(MmaDelegate.RESUMED_FROM_BACKGROUND);
+        MmaDelegate.notifyDefaultBrowserStatus(this);
     }
 
     @Override
     public void onStop() {
         super.onStop();
         if (mIsAbortingAppLaunch) {
             return;
         }

--- a/mobile/android/base/java/org/mozilla/gecko/mma/MmaDelegate.java
+++ b/mobile/android/base/java/org/mozilla/gecko/mma/MmaDelegate.java
@@ -24,17 +24,16 @@ import org.mozilla.gecko.R;
 import org.mozilla.gecko.Tab;
 import org.mozilla.gecko.Tabs;
 import org.mozilla.gecko.activitystream.homepanel.ActivityStreamConfiguration;
 import org.mozilla.gecko.fxa.FirefoxAccounts;
 import org.mozilla.gecko.preferences.GeckoPreferences;
 import org.mozilla.gecko.switchboard.SwitchBoard;
 import org.mozilla.gecko.util.ContextUtils;
 
-import java.lang.ref.WeakReference;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.UUID;
 
 
 public class MmaDelegate {
 
     public static final String READER_AVAILABLE = "E_Reader_Available";
@@ -45,39 +44,41 @@ public class MmaDelegate {
     public static final String INTERACT_WITH_SEARCH_URL_AREA = "E_Interact_With_Search_URL_Area";
     public static final String SCREENSHOT = "E_Screenshot";
     public static final String SAVED_LOGIN_AND_PASSWORD = "E_Saved_Login_And_Password";
     public static final String LAUNCH_BUT_NOT_DEFAULT_BROWSER = "E_Launch_But_Not_Default_Browser";
     public static final String LAUNCH_BROWSER = "E_Launch_Browser";
     public static final String RESUMED_FROM_BACKGROUND = "E_Resumed_From_Background";
     public static final String NEW_TAB = "E_Opened_New_Tab";
     public static final String DISMISS_ONBOARDING = "E_Dismiss_Onboarding";
-
+    public static final String CHANGED_DEFAULT_TO_FENNEC = "E_Changed_Default_To_Fennec";
 
     public static final String USER_ATT_FOCUS_INSTALLED = "Focus Installed";
     public static final String USER_ATT_KLAR_INSTALLED = "Klar Installed";
     public static final String USER_ATT_POCKET_INSTALLED = "Pocket Installed";
     public static final String USER_ATT_DEFAULT_BROWSER = "Default Browser";
     public static final String USER_ATT_SIGNED_IN = "Signed In Sync";
     public static final String USER_ATT_POCKET_TOP_SITES = "Pocket in Top Sites";
 
     public static final String PACKAGE_NAME_KLAR = "org.mozilla.klar";
     public static final String PACKAGE_NAME_FOCUS = "org.mozilla.focus";
     public static final String PACKAGE_NAME_POCKET = "com.ideashower.readitlater.pro";
 
     private static final String TAG = "MmaDelegate";
 
     public static final String KEY_ANDROID_PREF_STRING_LEANPLUM_DEVICE_ID = "android.not_a_preference.leanplum.device_id";
+    private static final String KEY_ANDROID_PREF_BOOLEAN_FENNEC_IS_DEFAULT = "android.not_a_preference.fennec.default.browser.status";
+
     private static final String DEBUG_LEANPLUM_DEVICE_ID = "8effda84-99df-11e7-abc4-cec278b6b50a";
 
     private static final MmaInterface mmaHelper = MmaConstants.getMma();
-    private static WeakReference<Context> applicationContext;
+    private static Context applicationContext;
 
     public static void init(Activity activity) {
-        applicationContext = new WeakReference<>(activity.getApplicationContext());
+        applicationContext = activity.getApplicationContext();
         // Since user attributes are gathered in Fennec, not in MMA implementation,
         // we gather the information here then pass to mmaHelper.init()
         // Note that generateUserAttribute always return a non null HashMap.
         final Map<String, Object> attributes = gatherUserAttributes(activity);
         final String deviceId = getDeviceId(activity);
         mmaHelper.setDeviceId(deviceId);
         PrefsHelper.setPref(GeckoPreferences.PREFS_MMA_DEVICE_ID, deviceId);
         // above two config setup required to be invoked before mmaHelper.init.
@@ -105,25 +106,45 @@ public class MmaDelegate {
         attributes.put(USER_ATT_POCKET_INSTALLED, ContextUtils.isPackageInstalled(context, PACKAGE_NAME_POCKET));
         attributes.put(USER_ATT_DEFAULT_BROWSER, isDefaultBrowser(context));
         attributes.put(USER_ATT_SIGNED_IN, FirefoxAccounts.firefoxAccountsExist(context));
         attributes.put(USER_ATT_POCKET_TOP_SITES, ActivityStreamConfiguration.isPocketRecommendingTopSites(context));
 
         return attributes;
     }
 
+    public static void notifyDefaultBrowserStatus(Activity activity) {
+        if (!isMmaEnabled(activity)) {
+            return;
+        }
+
+        final SharedPreferences sharedPreferences = activity.getPreferences(Context.MODE_PRIVATE);
+        final boolean isFennecDefaultBrowser = isDefaultBrowser(activity);
+
+        // Only if this is not the first run of LeanPlum and we previously tracked default browser status
+        // we can check for changes
+        if (sharedPreferences.contains(KEY_ANDROID_PREF_BOOLEAN_FENNEC_IS_DEFAULT)) {
+            // Will only inform LeanPlum of the event if Fennec was not previously the default browser
+            if (!sharedPreferences.getBoolean(KEY_ANDROID_PREF_BOOLEAN_FENNEC_IS_DEFAULT, true) && isFennecDefaultBrowser) {
+                track(CHANGED_DEFAULT_TO_FENNEC);
+            }
+        }
+
+        sharedPreferences.edit().putBoolean(KEY_ANDROID_PREF_BOOLEAN_FENNEC_IS_DEFAULT, isFennecDefaultBrowser).apply();
+    }
+
     public static void track(String event) {
-        if (applicationContext != null && isMmaEnabled(applicationContext.get())) {
+        if (applicationContext != null && isMmaEnabled(applicationContext)) {
             mmaHelper.event(event);
         }
     }
 
 
     public static void track(String event, long value) {
-        if (applicationContext != null && isMmaEnabled(applicationContext.get())) {
+        if (applicationContext != null && isMmaEnabled(applicationContext)) {
             mmaHelper.event(event, value);
         }
     }
 
     // isMmaEnabled should use pass-in context. The context comes from
     // 1. track(), it's called from UI (where we inject events). Context is from weak reference to Activity (assigned in init())
     // 2. handleGcmMessage(), it's called from GcmListenerService (where we handle GCM messages). Context is from the Service
     private static boolean isMmaEnabled(Context context) {

--- a/mobile/android/docs/mma.rst
+++ b/mobile/android/docs/mma.rst
@@ -155,16 +155,20 @@ List of current Events related data that
 * The user just dismissed on-boarding
 {
   "event" : "E_Dismiss_Onboarding"
 }
 * The user just resumed the app from background
 {
   "event" : "E_Resumed_From_Background"
 }
+* User set Fennec as default browser and resumed the app
+{
+  "event" : "E_Changed_Default_To_Fennec"
+}
 
 Deep Links:
 Deep links are actions that can point Fennec to open certain pages or load features such as `show bookmark list` or
 `open a SUMO page`. When users see a prompt Leanplum message, they can click the button(s) on it. These buttons can
 trigger the following deep links
 * Link to Set Default Browser settings (firefox://default_browser)
 * Link to specific Add-on page (http://link_to_the_add_on_page)
 * Link to sync signup/sign in (firefox://sign_up)