--- a/browser/components/sessionstore/test/browser_739805.js
+++ b/browser/components/sessionstore/test/browser_739805.js
@@ -24,17 +24,18 @@ function test() {
 
     ss.setTabState(tab, JSON.stringify(tabState));
     is(browser.__SS_restoreState, TAB_STATE_NEEDS_RESTORE, "tab needs restoring");
 
     let {formdata} = JSON.parse(ss.getTabState(tab));
     is(formdata && formdata.id["foo"], "bar", "tab state's formdata is valid");
 
     promiseTabRestored(tab).then(() => {
-      let input = browser.contentDocument.getElementById("foo");
-      is(input.value, "bar", "formdata has been restored correctly");
-      finish();
+      ContentTask.spawn(browser, null, function() {
+        let input = content.document.getElementById("foo");
+        is(input.value, "bar", "formdata has been restored correctly");
+      }).then(() => { finish(); });
     });
 
     // Restore the tab by selecting it.
     gBrowser.selectedTab = tab;
   });
 }