Bug 1648813 - disable browser_webarea.js on macos opt builds. r=jmaher

Differential Revision: https://phabricator.services.mozilla.com/D82254

accessible/tests/browser/mac/browser.ini

@@ -28,4 +28,5 @@ support-files =
 [browser_focus.js]
 [browser_whitespace.js]
 [browser_webarea.js]
+skip-if = os == 'mac' && !debug #1648813
 [browser_text_basics.js]