merge_pr_11623: noscript rules should not apply to non-HTML elements.

Differential Revision: https://phabricator.services.mozilla.com/D1749

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1470150
gecko-commit: e27f16329c725d807150863588ed572b2990c60c
gecko-integration-branch: mozilla-inbound
gecko-reviewers: heycam