User-Agent Stylesheet
In May 2025 all browsers should have removed the default styling for the h1 element when it is nested in a sectioning element (article, aside, nav, section). I went into Firefox Dev Editions user-agent style sheet and noticed that the styling for nested h1 elements is still the same. I'm wondering why that is the case, since I was under the impression that all the major browsers had completed make the necessary adjustments at the end of May 2025.
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Hi Paul, the MDN article says this was rolled out to all users in Firefox 140:
https://developer.mozilla.org/docs/Web/HTML/Reference/Elements/Heading_Elements => Browser Compatibility section
During the rollout, the change was controlled by a temporary preference. Can you check your about:config to confirm:
layout.css.h1-in-section-ua-styles.enabled => false
If you check the source of Firefox 140 and Firefox 141 beta, you'll notice the nesting is gated by the value of that preference at:
- https://searchfox.org/mozilla-release/source/layout/style/res/html.css#229
- https://searchfox.org/mozilla-beta/source/layout/style/res/html.css#237
A change has already been checked in to Nightly to delete the temporary preference and that rules section in Firefox 142: https://bugzilla.mozilla.org/show_bug.cgi?id=1976196
Since you are acquainted with this change, if you notice any problems with the implementation, please file a new bug.
Thanks for the quick response.
I checked the setting and you are right it is turned off.