--- a/testing/puppeteer/firefox/firefox_puppeteer/ui/browser/window.py
+++ b/testing/puppeteer/firefox/firefox_puppeteer/ui/browser/window.py
@@ -241,17 +241,17 @@ class BrowserWindow(BaseWindow):
         """
         def callback(win):
             # Prepare action which triggers the opening of the browser window
             if callable(trigger):
                 trigger(win)
             elif trigger == 'menu':
                 self.menubar.select_by_id('tools-menu', 'menu_pageInfo')
             elif trigger == 'shortcut':
-                if win.marionette.session_capabilities['platformName'] == 'WINDOWS_NT':
+                if win.marionette.session_capabilities['platformName'] == 'windows_nt':
                     raise ValueError('Page info shortcut not available on Windows.')
                 win.send_shortcut(win.get_entity('pageInfoCmd.commandkey'),
                                   accel=True)
             elif trigger == 'context_menu':
                 # TODO: Add once we can do right clicks
                 pass
             else:
                 raise ValueError('Unknown opening method: "%s"' % trigger)