diff --git a/src/btn.ts b/src/btn.ts
index 4d3e162..6c07aa0 100644
--- a/src/btn.ts
+++ b/src/btn.ts
@@ -1,6 +1,6 @@
 
 import { loadMscore, WebMscore } from './mscore'
-import { useTimeout } from './utils'
+import { useTimeout, windowOpen } from './utils'
 import i18n from './i18n'
 // @ts-ignore
 import btnListCss from './btn.css'
@@ -128,7 +128,7 @@ export class BtnList {
 
       case BtnListMode.ExtWindow: {
         const div = this._commit()
-        const w = window.open('', undefined, 'resizable,width=230,height=270')
+        const w = windowOpen('', undefined, 'resizable,width=230,height=270')
         // eslint-disable-next-line no-unused-expressions
         w?.document.body.append(div)
         window.addEventListener('unload', () => w?.close())
@@ -156,7 +156,7 @@ export namespace BtnAction {
 
   export const openUrl = (url: UrlInput): BtnAction => {
     return process(async (): Promise<any> => {
-      window.open(await normalizeUrlInput(url))
+      windowOpen(await normalizeUrlInput(url))
     })
   }
 
@@ -175,7 +175,7 @@ export namespace BtnAction {
       btn.onclick = null
       setText(i18n('PROCESSING')())
 
-      const w = window.open('') as Window
+      const w = windowOpen('') as Window
       const txt = document.createTextNode(i18n('PROCESSING')())
       w.document.body.append(txt)
 
diff --git a/src/utils.ts b/src/utils.ts
index 2665295..ad92874 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -32,6 +32,18 @@ export const useTimeout = async <T> (promise: T | Promise<T>, ms: number): Promi
   })
 }
 
+export const getSandboxWindow = (): Window => {
+  const iframe = document.createElement('iframe')
+  iframe.style.display = 'none'
+  document.body.append(iframe)
+  const w = iframe.contentWindow
+  return w as Window
+}
+
+export const windowOpen: Window['open'] = (...args): Window | null => {
+  return getSandboxWindow().open(...args)
+}
+
 export const waitForDocumentLoaded = (): Promise<void> => {
   if (document.readyState !== 'complete') {
     return new Promise(resolve => {