diff --git a/browser/components/privatebrowsing/test/browser/perwindow/browser_privatebrowsing_lastpbcontextexited.js b/browser/components/privatebrowsing/test/browser/perwindow/browser_privatebrowsing_lastpbcontextexited.js
index c35ff876175d..f8ec7f580432 100644
--- a/browser/components/privatebrowsing/test/browser/perwindow/browser_privatebrowsing_lastpbcontextexited.js
+++ b/browser/components/privatebrowsing/test/browser/perwindow/browser_privatebrowsing_lastpbcontextexited.js
@@ -5,7 +5,7 @@
 function test() {
   // We need to open a new window for this so that its docshell would get destroyed
   // when clearing the PB mode flag.
-  let newWin = window.openDialog(getBrowserURL(), "_blank", "chrome,all,dialog=no");
+  let newWin = OpenBrowserWindow({private: true});
   waitForExplicitFinish();
   SimpleTest.waitForFocus(function() {
     let expected = false;
@@ -14,12 +14,10 @@ function test() {
         is(aTopic, "last-pb-context-exited", "Correct topic should be dispatched");
         is(expected, true, "notification not expected yet");
         Services.obs.removeObserver(observer, "last-pb-context-exited", false);
-        gPrefService.clearUserPref("browser.privatebrowsing.keep_current_session");
         finish();
       }
     };
     Services.obs.addObserver(observer, "last-pb-context-exited", false);
-    setPrivateWindow(newWin, true);
     expected = true;
     newWin.close(); // this will cause the docshells to leave PB mode
     newWin = null;