stop the crash that causes #40306. the "first time start page" causes us

many problem on linux, not sure if it is related to that page, or
the redirect.  still investigating.

other changes here remove the crap code that forces you to go to
the checkin guidelines page and to see the account manager on start up
on debug builds.  this was preventing debug builds from seeing the problem.

after this change debug behaves like optimized, which is what we want.

r=mscott, a=granrose

docshell/base/nsDocShell.cpp

@@ -3244,6 +3244,9 @@ NS_IMETHODIMP nsDocShell::GetRootScrollableView(nsIScrollableView** aOutScrollVi
    NS_ENSURE_SUCCESS(viewManager->GetRootScrollableView(aOutScrollView),
       NS_ERROR_FAILURE);
 
+   NS_ASSERTION(*aOutScrollView, "no scroll view");
+   if (!*aOutScrollView) return NS_ERROR_FAILURE;
+
    return NS_OK;
 }