diff --git a/tests/selenium/pbtest.py b/tests/selenium/pbtest.py
index dad9aa8d52..521db5b18f 100644
--- a/tests/selenium/pbtest.py
+++ b/tests/selenium/pbtest.py
@@ -200,6 +200,10 @@ def firefox_manager(self):
         ffp.set_preference('extensions.webextensions.uuids', '{"%s": "%s"}' %
                            (self.info['extension_id'], self.info['uuid']))
 
+        # needed for test_referrer_header()
+        # https://bugzilla.mozilla.org/show_bug.cgi?id=1720294
+        ffp.set_preference('network.http.referer.disallowCrossSiteRelaxingDefault', False)
+
         for i in range(5):
             try:
                 opts = FirefoxOptions()