Bug 1638958 - Disable browser_label_and_icon.js on OS X 10.15 for frequent failures. r=intermittent-reviewers,ahal DONTBUILD

Differential Revision: https://phabricator.services.mozilla.com/D118297

browser/components/sessionstore/test/browser.ini

@@ -127,6 +127,7 @@ support-files = file_formdata_password.html
 [browser_label_and_icon.js]
 skip-if =
   apple_silicon  # high frequency intermittent
+  apple_catalina && !debug # Bug 1638958
 [browser_merge_closed_tabs.js]
 [browser_old_favicon.js]
 [browser_page_title.js]