Bug 1511134 - Skip web extension tests on GeckoView r=kmag

Differential Revision: https://phabricator.services.mozilla.com/D14559

--HG--
extra : moz-landing-system : lando

mobile/android/components/extensions/test/mochitest/mochitest.ini

@@ -12,6 +12,7 @@ support-files =
   file_slowed_document.sjs
   head.js
 tags = webextensions
+skip-if = !isFennec
 
 [test_ext_all_apis.html]
 [test_ext_downloads_saveAs.html]