diff --git a/src/content_scripts/main.js b/src/content_scripts/main.js
index 50a30f844..ce9b29633 100644
--- a/src/content_scripts/main.js
+++ b/src/content_scripts/main.js
@@ -81,7 +81,6 @@
 
     const { nonce } = [...document.scripts].find(script => script.getAttributeNames().includes('nonce'));
     const script = document.createElement('script');
-    script.type = 'module';
     script.nonce = nonce;
     script.src = browser.runtime.getURL('/main_world/index.js');
     document.documentElement.append(script);
diff --git a/src/main_world/index.js b/src/main_world/index.js
index 63f12c1a2..5d7bc1d12 100644
--- a/src/main_world/index.js
+++ b/src/main_world/index.js
@@ -1,34 +1,38 @@
-const moduleCache = {};
+'use strict';
 
-document.documentElement.addEventListener('xkitinjectionrequest', async event => {
-  const { detail, target } = event;
-  const { id, path, args } = JSON.parse(detail);
+{
+  const moduleCache = {};
 
-  try {
-    moduleCache[path] ??= await import(path);
-    const func = moduleCache[path].default;
+  document.documentElement.addEventListener('xkitinjectionrequest', async event => {
+    const { detail, target } = event;
+    const { id, path, args } = JSON.parse(detail);
 
-    if (target.isConnected === false) return;
+    try {
+      moduleCache[path] ??= await import(path);
+      const func = moduleCache[path].default;
 
-    const result = await func.apply(target, args);
-    target.dispatchEvent(
-      new CustomEvent('xkitinjectionresponse', { detail: JSON.stringify({ id, result }) })
-    );
-  } catch (exception) {
-    target.dispatchEvent(
-      new CustomEvent('xkitinjectionresponse', {
-        detail: JSON.stringify({
-          id,
-          exception: {
-            message: exception.message,
-            name: exception.name,
-            stack: exception.stack,
-            ...exception
-          }
+      if (target.isConnected === false) return;
+
+      const result = await func.apply(target, args);
+      target.dispatchEvent(
+        new CustomEvent('xkitinjectionresponse', { detail: JSON.stringify({ id, result }) })
+      );
+    } catch (exception) {
+      target.dispatchEvent(
+        new CustomEvent('xkitinjectionresponse', {
+          detail: JSON.stringify({
+            id,
+            exception: {
+              message: exception.message,
+              name: exception.name,
+              stack: exception.stack,
+              ...exception
+            }
+          })
         })
-      })
-    );
-  }
-});
+      );
+    }
+  });
 
-document.documentElement.dispatchEvent(new CustomEvent('xkitinjectionready'));
+  document.documentElement.dispatchEvent(new CustomEvent('xkitinjectionready'));
+}