[py] Use XWayland for internal Python Firefox tests

Author: cgoldberg

py/conftest.py

@@ -154,6 +154,9 @@ def fin():
     if driver_instance is None:
         if driver_class == "Firefox":
             options = get_options(driver_class, request.config)
+            # There are issues with window size/position when running Firefox
+            # under Wayland, so we use XWayland instead.
+            os.environ['MOZ_ENABLE_WAYLAND'] = '0'
         if driver_class == "Chrome":
             options = get_options(driver_class, request.config)
         if driver_class == "Edge":