Fix Firefox to be more reliable on versions over 45

* Firefox behaves differently between an ActionChains click and a "real"
  click. The ActionChains click does not try to wait for page navigation
  as such, navigations often fail because the page is changed from under
  it.
* We now use a "real" click if a navigation has been requested. This now
  also initiates a sleep for 1s immediately after we instruct marionette
  to click. This is then enough time for any CSS animations to finish up
  before we continue running any more selenium methods to check for page
  objects to be displayed.

src/widgetastic/browser.py

@@ -4,7 +4,6 @@
 import inspect
 import six
 import time
-
 from cached_property import cached_property
 from collections import namedtuple
 from jsmin import jsmin
@@ -23,9 +22,8 @@
     StaleElementReferenceException, NoAlertPresentException, LocatorNotImplemented,
     WebDriverException)
 from .log import create_widget_logger, null_logger
-from .xpath import normalize_space
 from .utils import crop_string_middle
-
+from .xpath import normalize_space
 
 Size = namedtuple('Size', ['width', 'height'])
 Location = namedtuple('Location', ['x', 'y'])
@@ -351,10 +349,15 @@ def click(self, locator, *args, **kwargs):
         """
         self.logger.debug('click: %r', locator)
         ignore_ajax = kwargs.pop('ignore_ajax', False)
+        nav_click = kwargs.pop('nav_click', False)
         el = self.move_to_element(locator, *args, **kwargs)
         self.plugin.before_click(el)
         # and then click on current mouse position
-        self.perform_click()
+        if nav_click and self.browser_type.lower() == 'firefox' and self.browser_version > 52:
+            el.click()
+            time.sleep(1)
+        else:
+            self.perform_click()
         if not ignore_ajax:
             try:
                 self.plugin.ensure_page_safe()