Follow-up to bug 810180 - Reset the homepage to about:blank when opening new windows in the test; r=jdm

DONTBUILD because this is NPOTB in global PB builds

browser/components/search/test/browser_private_search_perwindowpb.js

@@ -3,6 +3,10 @@
 // whether there is an autocomplete entry for the private search.
 
 function test() {
+  // Don't use about:home as the homepage for new windows
+  Services.prefs.setIntPref("browser.startup.page", 0);
+  registerCleanupFunction(function() Services.prefs.clearUserPref("browser.startup.page"));
+
   waitForExplicitFinish();
 
   let engineURL =