--- a/mobile/android/base/java/org/mozilla/gecko/BrowserApp.java
+++ b/mobile/android/base/java/org/mozilla/gecko/BrowserApp.java
@@ -1367,16 +1367,18 @@ public class BrowserApp extends GeckoApp
                 final SharedPreferences sharedPrefs = GeckoSharedPrefs.forProfileName(BrowserApp.this, profile.getName());
                 FileCleanupController.startIfReady(BrowserApp.this, sharedPrefs, profile.getDir().getAbsolutePath());
             }
         });
 
         for (final BrowserAppDelegate delegate : delegates) {
             delegate.onStart(this);
         }
+
+        MmaDelegate.informDefaultBrowserStatus();
     }
 
     @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
@@ -44,16 +44,17 @@ public class MmaDelegate {
     public static final String OPENED_BOOKMARK = "E_Opened_Bookmark";
     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 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";
@@ -64,30 +65,32 @@ public class MmaDelegate {
 
     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 DEBUG_LEANPLUM_DEVICE_ID = "8effda84-99df-11e7-abc4-cec278b6b50a";
 
     private static final MmaInterface mmaHelper = MmaConstants.getMma();
     private static WeakReference<Context> applicationContext;
+    private static boolean defaultBrowserStatus;
 
     public static void init(Activity activity) {
         applicationContext = new WeakReference<>(activity.getApplicationContext());
+        defaultBrowserStatus = isDefaultBrowser(activity);
         // 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.
         mmaHelper.init(activity, attributes);
 
-        if (!isDefaultBrowser(activity)) {
+        if (!defaultBrowserStatus) {
             mmaHelper.event(MmaDelegate.LAUNCH_BUT_NOT_DEFAULT_BROWSER);
         }
         mmaHelper.event(MmaDelegate.LAUNCH_BROWSER);
 
     }
 
     public static void stop() {
         mmaHelper.stop();
@@ -97,23 +100,33 @@ public class MmaDelegate {
     @NonNull
     private static Map<String, Object> gatherUserAttributes(final Context context) {
 
         final Map<String, Object> attributes = new HashMap<>();
 
         attributes.put(USER_ATT_FOCUS_INSTALLED, ContextUtils.isPackageInstalled(context, PACKAGE_NAME_FOCUS));
         attributes.put(USER_ATT_KLAR_INSTALLED, ContextUtils.isPackageInstalled(context, PACKAGE_NAME_KLAR));
         attributes.put(USER_ATT_POCKET_INSTALLED, ContextUtils.isPackageInstalled(context, PACKAGE_NAME_POCKET));
-        attributes.put(USER_ATT_DEFAULT_BROWSER, isDefaultBrowser(context));
+        attributes.put(USER_ATT_DEFAULT_BROWSER, defaultBrowserStatus);
         attributes.put(USER_ATT_SIGNED_IN, FirefoxAccounts.firefoxAccountsExist(context));
         attributes.put(USER_ATT_POCKET_TOP_SITES, ActivityStreamConfiguration.isPocketRecommendingTopSites(context));
 
         return attributes;
     }
 
+    public static void informDefaultBrowserStatus() {
+        // Method may be called before class was initialized
+        if (applicationContext == null || applicationContext.get() == null) return;
+
+        if (!defaultBrowserStatus && isDefaultBrowser(applicationContext.get())) {
+            defaultBrowserStatus = !defaultBrowserStatus;
+            track(CHANGED_DEFAULT_TO_FENNEC);
+        }
+    }
+
     public static void track(String event) {
         if (applicationContext != null && isMmaEnabled(applicationContext.get())) {
             mmaHelper.event(event);
         }
     }
 
 
     public static void track(String event, long value) {

--- a/mobile/android/docs/mma.rst
+++ b/mobile/android/docs/mma.rst
@@ -150,16 +150,20 @@ List of current Events related data that
 * General app start event
 {
   "event" : "E_Launch_Browser"
 }
 * The user just dismissed on-boarding
 {
   "event" : "E_Dismiss_Onboarding"
 }
+* 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)