--- a/docshell/test/browser/browser_bug1347823.js
+++ b/docshell/test/browser/browser_bug1347823.js
@@ -47,18 +47,20 @@ add_task(async function testExpiredCache
         content.document.body.textContent = "modified";
       });
 
       // Load a random page.
       BrowserTestUtils.loadURI(browser, "data:text/html;charset=utf-8,page2");
       await BrowserTestUtils.browserLoaded(browser);
 
       // Wait for 3 times of expiration timeout, hopefully it's evicted...
-      await new Promise(resolve => {
-        setTimeout(resolve, 3000);
+      await ContentTask.spawn(browser, null, () => {
+        return new Promise(resolve => {
+          content.setTimeout(resolve, 3000);
+        });
       });
 
       // Go back and verify text content.
       let awaitPageShow = BrowserTestUtils.waitForContentEvent(browser, "pageshow");
       browser.goBack();
       await awaitPageShow;
       await ContentTask.spawn(browser, null, () => {
         is(content.document.body.textContent, "page1");