diff --git a/app/src/common/shared/org/mozilla/vrbrowser/browser/engine/Session.java b/app/src/common/shared/org/mozilla/vrbrowser/browser/engine/Session.java
index d0796eee7..712455b33 100644
--- a/app/src/common/shared/org/mozilla/vrbrowser/browser/engine/Session.java
+++ b/app/src/common/shared/org/mozilla/vrbrowser/browser/engine/Session.java
@@ -286,7 +286,7 @@ public void setHistoryDelegate(GeckoSession.HistoryDelegate aDelegate) {
     }
 
     public void addNavigationListener(GeckoSession.NavigationDelegate aListener) {
-        mNavigationListeners.add(aListener);
+        mNavigationListeners.addIfAbsent(aListener);
         dumpState(aListener);
     }
 
@@ -295,7 +295,7 @@ public void removeNavigationListener(GeckoSession.NavigationDelegate aListener)
     }
 
     public void addProgressListener(GeckoSession.ProgressDelegate aListener) {
-        mProgressListeners.add(aListener);
+        mProgressListeners.addIfAbsent(aListener);
         dumpState(aListener);
     }
 
@@ -304,7 +304,7 @@ public void removeProgressListener(GeckoSession.ProgressDelegate aListener) {
     }
 
     public void addContentListener(GeckoSession.ContentDelegate aListener) {
-        mContentListeners.add(aListener);
+        mContentListeners.addIfAbsent(aListener);
         dumpState(aListener);
     }
 
@@ -313,7 +313,7 @@ public void removeContentListener(GeckoSession.ContentDelegate aListener) {
     }
 
     public void addSessionChangeListener(SessionChangeListener aListener) {
-        mSessionChangeListeners.add(aListener);
+        mSessionChangeListeners.addIfAbsent(aListener);
     }
 
     public void removeSessionChangeListener(SessionChangeListener aListener) {
@@ -321,7 +321,7 @@ public void removeSessionChangeListener(SessionChangeListener aListener) {
     }
 
     public void addTextInputListener(GeckoSession.TextInputDelegate aListener) {
-        mTextInputListeners.add(aListener);
+        mTextInputListeners.addIfAbsent(aListener);
     }
 
     public void removeTextInputListener(GeckoSession.TextInputDelegate aListener) {
@@ -329,7 +329,7 @@ public void removeTextInputListener(GeckoSession.TextInputDelegate aListener) {
     }
 
     public void addVideoAvailabilityListener(VideoAvailabilityListener aListener) {
-        mVideoAvailabilityListeners.add(aListener);
+        mVideoAvailabilityListeners.addIfAbsent(aListener);
         dumpState(aListener);
     }
 
@@ -338,7 +338,7 @@ public void removeVideoAvailabilityListener(VideoAvailabilityListener aListener)
     }
 
     public void addSelectionActionListener(GeckoSession.SelectionActionDelegate aListener) {
-        mSelectionActionListeners.add(aListener);
+        mSelectionActionListeners.addIfAbsent(aListener);
     }
 
     public void removeSelectionActionListener(GeckoSession.ContentDelegate aListener) {
@@ -346,7 +346,7 @@ public void removeSelectionActionListener(GeckoSession.ContentDelegate aListener
     }
 
     public void addBitmapChangedListener(BitmapChangedListener aListener) {
-        mBitmapChangedListeners.add(aListener);
+        mBitmapChangedListeners.addIfAbsent(aListener);
     }
 
     public void removeBitmapChangedListener(BitmapChangedListener aListener) {
@@ -354,7 +354,7 @@ public void removeBitmapChangedListener(BitmapChangedListener aListener) {
     }
 
     public void addWebXRStateChangedListener(WebXRStateChangedListener aListener) {
-        mWebXRStateListeners.add(aListener);
+        mWebXRStateListeners.addIfAbsent(aListener);
         dumpState(aListener);
     }
 
@@ -363,7 +363,7 @@ public void removeWebXRStateChangedListener(WebXRStateChangedListener aListener)
     }
 
     public void addPopUpStateChangedListener(PopUpStateChangedListener aListener) {
-        mPopUpStateStateListeners.add(aListener);
+        mPopUpStateStateListeners.addIfAbsent(aListener);
         dumpState(aListener);
     }
 
@@ -372,7 +372,7 @@ public void removePopUpStateChangedListener(PopUpStateChangedListener aListener)
     }
 
     public void addDrmStateChangedListener(DrmStateChangedListener aListener) {
-        mDrmStateStateListeners.add(aListener);
+        mDrmStateStateListeners.addIfAbsent(aListener);
         dumpState(aListener);
     }
 
diff --git a/app/src/common/shared/org/mozilla/vrbrowser/ui/widgets/WindowWidget.java b/app/src/common/shared/org/mozilla/vrbrowser/ui/widgets/WindowWidget.java
index 31866cb51..4b933ec53 100644
--- a/app/src/common/shared/org/mozilla/vrbrowser/ui/widgets/WindowWidget.java
+++ b/app/src/common/shared/org/mozilla/vrbrowser/ui/widgets/WindowWidget.java
@@ -1158,12 +1158,17 @@ public void onCurrentSessionChange(GeckoSession aOldSession, GeckoSession aSessi
 
     @Override
     public void onStackSession(Session aSession) {
+        if (aSession == mSession) {
+            Log.e(LOGTAG, "Attempting to stack same session.");
+            return;
+        }
         // e.g. tab opened via window.open()
         aSession.updateLastUse();
         Session current = mSession;
         setupListeners(aSession);
         setSession(aSession);
         SessionStore.get().setActiveSession(aSession);
+        aSession.setActive(true);
         current.captureBackgroundBitmap(getWindowWidth(), getWindowHeight()).thenAccept(aVoid -> current.setActive(false));
         mWidgetManager.getWindows().showTabAddedNotification();