In case you were actually looking for an answer to your question, it's in the article: > To test in Firefox with the new behavior, set layout.css.h1-in-section

In case you were actually looking for an answer to your question, it's in the article: > To test in Firefox with the new behavior, set layout.css.h1-in-section-ua-styles.enabled to false in about:config. Gbd article doesn't specify how to test in Chrome (probably something in chrome://flags), but you can read the deprecation warnings dumped into your console. You may need to enable them in your default log level. If so, there may be a lot of other behaviour that you'll probably want to fix.