Bug 1615184 - Disable intermittent test_ext_cookies.html for TSan. r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D62721

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

toolkit/components/extensions/test/mochitest/mochitest-common.ini

@@ -82,6 +82,7 @@ skip-if = os == 'android' # Android does not support multiple windows.
 [test_ext_contentscript_permission.html]
 skip-if = tsan # Times out on TSan, bug 1612707
 [test_ext_cookies.html]
+skip-if = tsan # Times out on TSan intermittently, bug 1615184
 [test_ext_cookies_containers.html]
 [test_ext_cookies_expiry.html]
 [test_ext_cookies_first_party.html]