2 files changed, 13 insertions, 3 deletions
diff --git a/dom/base/CustomElementRegistry.h b/dom/base/CustomElementRegistry.h
index c180a10af..51c97fd5e 100644
--- a/dom/base/CustomElementRegistry.h
+++ b/dom/base/CustomElementRegistry.h
@@ -472,15 +472,24 @@ public:
 
 class MOZ_RAII AutoCEReaction final {
   public:
-    explicit AutoCEReaction(CustomElementReactionsStack* aReactionsStack)
-      : mReactionsStack(aReactionsStack) {
+    // JSContext is allowed to be a nullptr if we are guaranteeing that we're
+    // not doing something that might throw but not finish reporting a JS
+    // exception during the lifetime of the AutoCEReaction.
+    AutoCEReaction(CustomElementReactionsStack* aReactionsStack, JSContext* aCx)
+      : mReactionsStack(aReactionsStack)
+      , mCx(aCx) {
       mReactionsStack->CreateAndPushElementQueue();
     }
     ~AutoCEReaction() {
+      Maybe<JS::AutoSaveExceptionState> ases;
+      if (mCx) {
+        ases.emplace(mCx);
+      }
       mReactionsStack->PopAndInvokeElementQueue();
     }
   private:
     RefPtr<CustomElementReactionsStack> mReactionsStack;
+    JSContext* mCx;
 };
 
 } // namespace dom
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index 9043e409a..f3e492589 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -5809,7 +5809,8 @@ nsDocument::RegisterElement(JSContext* aCx, const nsAString& aType,
     return;
   }
 
-  AutoCEReaction ceReaction(this->GetDocGroup()->CustomElementReactionsStack());
+  AutoCEReaction ceReaction(this->GetDocGroup()->CustomElementReactionsStack(),
+                            aCx);
   // Unconditionally convert TYPE to lowercase.
   nsAutoString lcType;
   nsContentUtils::ASCIIToLower(aType, lcType);