https://hg-edge.mozilla.org/mozilla-central/rev/d4b3eb4f76e8

Index: python/mozbuild/mozbuild/vendor/vendor_python.py
--- python/mozbuild/mozbuild/vendor/vendor_python.py.orig
+++ python/mozbuild/mozbuild/vendor/vendor_python.py
@@ -40,6 +40,10 @@ EXCLUDED_PACKAGES = {
     # modified 'dummy' version of it so that the dependency checks still succeed, but
     # if it ever is attempted to be used, it will fail gracefully.
     "ansicon",
+    # jsonschema 4.17.3 is incompatible with Python 3.14+,
+    # but later versions use a dependency with Rust components, which we thus can't vendor.
+    # For now we apply the minimal patch to jsonschema to make it work again.
+    "jsonschema",
 }
 
 
