diff --git a/framework/core/js/package.json b/framework/core/js/package.json
index 6e8909151e..bb2ce5580d 100644
--- a/framework/core/js/package.json
+++ b/framework/core/js/package.json
@@ -18,7 +18,8 @@
         "nanoid": "^3.1.30",
         "punycode": "^2.1.1",
         "textarea-caret": "^3.1.0",
-        "throttle-debounce": "^3.0.1"
+        "throttle-debounce": "^3.0.1",
+        "xslt-polyfill": "^1.0.16"
     },
     "devDependencies": {
         "@flarum/jest-config": "^2.0.0",
diff --git a/framework/core/src/Formatter/Formatter.php b/framework/core/src/Formatter/Formatter.php
index 51019bfe47..5a4e921060 100644
--- a/framework/core/src/Formatter/Formatter.php
+++ b/framework/core/src/Formatter/Formatter.php
@@ -190,10 +190,61 @@ protected function getRenderer(): Renderer
 
     /**
      * Get the formatter JavaScript.
+     *
+     * Injects XSLT polyfill inline before s9e code to support browsers
+     * that have removed native XSLT support (Chrome 155+, Nov 2026).
+     *
+     * @TODO: Remove polyfill injection when s9e/textformatter has a solution for XSLT removal.
+     * @see https://github.com/s9e/TextFormatter/issues/250
      */
     public function getJs(): string
     {
-        return $this->getComponent('js');
+        $s9eJs = $this->getComponent('js');
+
+        // Try to load XSLT polyfill
+        // Path 1: Published package (core/js/node_modules)
+        $polyfillPath = __DIR__.'/../../js/node_modules/xslt-polyfill/xslt-polyfill.min.js';
+
+        if (! file_exists($polyfillPath)) {
+            // Path 2: Monorepo hoisted (framework/node_modules)
+            $polyfillPath = __DIR__.'/../../../../node_modules/xslt-polyfill/xslt-polyfill.min.js';
+        }
+
+        if (! file_exists($polyfillPath)) {
+            // Polyfill not available, return s9e JS without it
+            return $s9eJs;
+        }
+
+        $polyfillJs = file_get_contents($polyfillPath);
+
+        // Inject polyfill inline before s9e code
+        return <<<JS
+// XSLT Polyfill for Chrome 155+ (Nov 2026)
+// Chrome is removing native XSLT support. This polyfill ensures s9e TextFormatter
+// continues to work for live preview functionality.
+(function() {
+    var xsltWorks = false;
+
+    if (typeof window !== 'undefined' && window.XSLTProcessor) {
+        try {
+            // Test if XSLTProcessor can actually be instantiated
+            // (constructor exists but throws when XSLT is disabled)
+            new XSLTProcessor();
+            xsltWorks = true;
+        } catch (e) {
+            // XSLTProcessor exists but is disabled
+        }
+    }
+
+    if (!xsltWorks) {
+        // Load polyfill
+        $polyfillJs
+    }
+})();
+
+// s9e TextFormatter code
+$s9eJs
+JS;
     }
 
     protected function configureDefaultsOnLinks(string $xml): string
diff --git a/yarn.lock b/yarn.lock
index 5c5b01f307..54321a7a34 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -5691,6 +5691,11 @@ xmlchars@^2.2.0:
   resolved "https://registry.yarnpkg.com/xmlchars/-/xmlchars-2.2.0.tgz#060fe1bcb7f9c76fe2a17db86a9bc3ab894210cb"
   integrity sha512-JZnDKK8B0RCDw84FNdDAIpZK+JuJw+s7Lz8nksI7SIuU3UXJJslUthsi+uWBUYOwPFwW7W7PRLRfUKpxjtjFCw==
 
+xslt-polyfill@^1.0.16:
+  version "1.0.16"
+  resolved "https://registry.yarnpkg.com/xslt-polyfill/-/xslt-polyfill-1.0.16.tgz#86edb1767bc005ce5c5465be309d266785d4a5d6"
+  integrity sha512-lz0pP+N5X552mZ3IL5qM/7pHwPYNLEF973fFdqnHchm638gw6zWlwroAChnNOzAYLDj0CBvshtupDjqCjZpmXw==
+
 y18n@^5.0.5:
   version "5.0.8"
   resolved "https://registry.yarnpkg.com/y18n/-/y18n-5.0.8.tgz#7f4934d0f7ca8c56f95314939ddcd2dd91ce1d55"