--- a/js/xpconnect/src/XPCJSRuntime.cpp
+++ b/js/xpconnect/src/XPCJSRuntime.cpp
@@ -2895,16 +2895,17 @@ XPCJSRuntime::Initialize(JSContext* cx)
     mPrevGCSliceCallback = JS::SetGCSliceCallback(cx, GCSliceCallback);
     mPrevDoCycleCollectionCallback = JS::SetDoCycleCollectionCallback(cx,
             DoCycleCollectionCallback);
     JS_AddFinalizeCallback(cx, FinalizeCallback, nullptr);
     JS_AddWeakPointerZonesCallback(cx, WeakPointerZonesCallback, this);
     JS_AddWeakPointerCompartmentCallback(cx, WeakPointerCompartmentCallback, this);
     JS_SetWrapObjectCallbacks(cx, &WrapObjectCallbacks);
     js::SetPreserveWrapperCallback(cx, PreserveWrapper);
+    JS_InitReadPrincipalsCallback(cx, nsJSPrincipals::ReadPrincipals);
     JS_SetAccumulateTelemetryCallback(cx, AccumulateTelemetryCallback);
     JS_SetSetUseCounterCallback(cx, SetUseCounterCallback);
     js::SetWindowProxyClass(cx, &OuterWindowProxyClass);
     js::SetXrayJitInfo(&gXrayJitInfo);
     JS::SetProcessLargeAllocationFailureCallback(OnLargeAllocationFailureCallback);
 
     // The JS engine needs to keep the source code around in order to implement
     // Function.prototype.toSource(). It'd be nice to not have to do this for