diff --git a/src/templates/cke-configs/_edit.twig b/src/templates/cke-configs/_edit.twig
index c1485786..0880ffff 100644
--- a/src/templates/cke-configs/_edit.twig
+++ b/src/templates/cke-configs/_edit.twig
@@ -186,30 +186,46 @@
   {% endblock %}
 {% endembed %}
 
-{% script with {type: 'module'} %}
-import {ConfigOptions, ToolbarBuilder} from '@craftcms/ckeditor-config';
-{{ importStatements|raw }}
-
-const configOptions = new ConfigOptions("{{ configOptionsId }}", "{{ jsonSchemaUri }}");
-new ToolbarBuilder("{{  toolbarBuilderId }}", "{{ containerId }}", configOptions, [{{ plugins | join(',') }}]);
-
-(() => {
-  // Register the config options JSON schema
-  const jsonSchemaUri = {{ jsonSchemaUri|json_encode|raw }};
-  const schema = JSON.parse(JSON.stringify({{jsonSchema|json_encode|raw}}));
-
-  monaco.languages.json.jsonDefaults.setDiagnosticsOptions({
-    validate: true,
-    schemas: [
-      {
-        uri: jsonSchemaUri,
-        fileMatch: [jsonSchemaUri],
-        schema: schema,
-      },
-    ],
-  });
-})()
-{% endscript %}
+<script type="module">
+  import {ConfigOptions, ToolbarBuilder} from '@craftcms/ckeditor-config';
+  {{ importStatements|raw }}
+
+  function initializeConfig() {
+    const configOptions = new ConfigOptions("{{ configOptionsId }}", "{{ jsonSchemaUri }}");
+    new ToolbarBuilder("{{ toolbarBuilderId }}", "{{ containerId }}", configOptions, [{{ plugins | join(',') }}]);
+
+    (() => {
+      // Register the config options JSON schema
+      const jsonSchemaUri = {{ jsonSchemaUri|json_encode|raw }};
+      const schema = JSON.parse(JSON.stringify({{ jsonSchema|json_encode|raw }}));
+
+      monaco.languages.json.jsonDefaults.setDiagnosticsOptions({
+        validate: true,
+        schemas: [
+          {
+            uri: jsonSchemaUri,
+            fileMatch: [jsonSchemaUri],
+            schema: schema,
+          },
+        ],
+      });
+    })();
+  }
+
+  /**
+   * This is not ideal, but when loading the config in a slideout (seemingly only in FireFox)
+   * this module code can run `window.monacoEditorInstances` has been created.
+   */
+  function checkWindow() {
+    if (typeof window.monacoEditorInstances === 'undefined') {
+      setTimeout(checkWindow, 100);
+    } else {
+      initializeConfig();
+    }
+  }
+
+  checkWindow();
+</script>
 
 {{ codeEditor.textareaField(
   {