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FF139 Relnote - Escape < and > in attributes when serializing HTML #39364

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FF139 Relnote - Escape < and > in attributes when serializing HTML #39364

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FF139 Relnote: ExprFeat Escape < and > in attributes when serialize HTML
hamishwillee May 2, 2025
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hamishwillee May 5, 2025
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4 changes: 4 additions & 0 deletions files/en-us/mozilla/firefox/releases/139/index.md
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Expand Up @@ -68,6 +68,10 @@ This article provides information about the changes in Firefox 139 that affect d

These features are newly shipped in Firefox 139 but are disabled by default. To experiment with them, search for the appropriate preference on the `about:config` page and set it to `true`. You can find more such features on the [Experimental features](/en-US/docs/Mozilla/Firefox/Experimental_features) page.

- **Support for escaping `<` and `>` in attributes when serializing HTML**: `dom.security.html_serialization_escape_lt_gt`.
Firefox now replaces the `<` and `>` characters with `&lt;` and `&gt;`, respectively, in attributes when serializing HTML. This helps prevent certain exploits where HTML is serialized and then injected back into the DOM.
The affected methods and properties are: {{domxref("Element.innerHTML")}}, {{domxref("Element.outerHTML")}}, {{domxref("Element.getHTML()")}}, {{domxref("ShadowRoot.innerHTML")}}, and {{domxref("ShadowRoot.getHTML()")}}. ([Firefox bug 1941347](https://bugzil.la/1941347)).

## Older versions

{{Firefox_for_developers}}