diff --git a/ext/fg/js/popup-proxy-host.js b/ext/fg/js/popup-proxy-host.js
index fdb54cdd..49123ee1 100644
--- a/ext/fg/js/popup-proxy-host.js
+++ b/ext/fg/js/popup-proxy-host.js
@@ -47,7 +47,7 @@ class PopupProxyHost {
         ]));
     }
 
-    getOrCreatePopup(id=null, parentId=null, depth=0) {
+    getOrCreatePopup(id=null, parentId=null, depth=null) {
         // Find by existing id
         if (id !== null) {
             const popup = this._popups.get(id);
@@ -77,10 +77,12 @@ class PopupProxyHost {
 
         // Create new popup
         if (parent !== null) {
-            if (depth !== 0) {
+            if (depth !== null) {
                 throw new Error('Depth cannot be set when parent exists');
             }
             depth = parent.depth + 1;
+        } else if (depth === null) {
+            depth = 0;
         }
         const popup = new Popup(id, depth, this._frameIdPromise);
         if (parent !== null) {