UPD: make selenium tests headless by default.

dav_base/tests/generic.py

@@ -201,6 +201,7 @@ class UrlsTestCase(SimpleTestCase):
 
 
 class SeleniumTestCase(StaticLiveServerTestCase):
+    headless = True
     window_width = 1024
     window_height = 768
 
@@ -213,6 +214,8 @@ class SeleniumTestCase(StaticLiveServerTestCase):
     @property
     def selenium(self):
         if self._driver is None:
+            if self.headless:
+                self._driver_options.add_argument('--headless')
             self._driver = webdriver.Firefox(options=self._driver_options)
             if self.quit_selenium is None:
                 self.quit_selenium = True