diff --git a/browser/devtools/webide/content/webide.js b/browser/devtools/webide/content/webide.js
index 1b2838dd8ca3..695570bd9c3c 100644
--- a/browser/devtools/webide/content/webide.js
+++ b/browser/devtools/webide/content/webide.js
@@ -632,7 +632,7 @@ let UI = {
     splitter.removeAttribute("hidden");
 
     let iframe = document.createElement("iframe");
-    document.querySelector("window").insertBefore(iframe, splitter.nextSibling);
+    document.querySelector("notificationbox").insertBefore(iframe, splitter.nextSibling);
     let host = devtools.Toolbox.HostType.CUSTOM;
     let options = { customIframe: iframe };
     this.toolboxIframe = iframe;
diff --git a/browser/devtools/webide/content/webide.xul b/browser/devtools/webide/content/webide.xul
index cc481acb6721..0253b3364ba0 100644
--- a/browser/devtools/webide/content/webide.xul
+++ b/browser/devtools/webide/content/webide.xul
@@ -181,10 +181,9 @@
       <iframe id="deck-panel-runtimedetails" flex="1" src="runtimedetails.xhtml"/>
       <iframe id="deck-panel-monitor" flex="1" lazysrc="monitor.xhtml"/>
     </deck>
+    <splitter hidden="true" class="devtools-horizontal-splitter" orient="vertical"/>
+    <!-- toolbox iframe will be inserted here -->
   </notificationbox>
 
-  <splitter hidden="true" class="devtools-horizontal-splitter" orient="vertical"/>
-
-  <!-- toolbox iframe will be inserted here -->
 
 </window>