--- a/editor/spellchecker/EditorSpellCheck.cpp
+++ b/editor/spellchecker/EditorSpellCheck.cpp
@@ -891,17 +891,20 @@ EditorSpellCheck::DictionaryFetched(Dict
           // list.
           self->DeleteSuggestedWordList();
 
           self->EndUpdateDictionary();
           if (fetcher->mCallback) {
             fetcher->mCallback->EditorSpellCheckDone();
           }
         },
-        [self, fetcher]() {
+        [self, fetcher](nsresult aError) {
+          if (aError == NS_ERROR_ABORT) {
+            return;
+          }
           // May be dictionary was uninstalled ?
           // Clear the content preference and continue.
           ClearCurrentDictionary(self->mEditor);
 
           // Priority 2 or later will handled by the following
           self->SetFallbackDictionary(fetcher);
         });
       return NS_OK;

--- a/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineChild.cpp
+++ b/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineChild.cpp
@@ -12,44 +12,56 @@ RemoteSpellcheckEngineChild::RemoteSpell
 {
 }
 
 RemoteSpellcheckEngineChild::~RemoteSpellcheckEngineChild()
 {
   // null out the owner's SpellcheckEngineChild to prevent state corruption
   // during shutdown
   mOwner->DeleteRemoteEngine();
+
+  // ensure we don't leak any promise holders for which we haven't yet
+  // received responses
+  for (UniquePtr<MozPromiseHolder<GenericPromise>>& promiseHolder : mResponsePromises) {
+    promiseHolder->RejectIfExists(NS_ERROR_ABORT, __func__);
+  }
 }
 
 RefPtr<GenericPromise>
 RemoteSpellcheckEngineChild::SetCurrentDictionaryFromList(
   const nsTArray<nsString>& aList)
 {
-  MozPromiseHolder<GenericPromise>* promiseHolder =
-    new MozPromiseHolder<GenericPromise>();
+  UniquePtr<MozPromiseHolder<GenericPromise>> promiseHolder =
+    MakeUnique<MozPromiseHolder<GenericPromise>>();
   if (!SendSetDictionaryFromList(
          aList,
-         reinterpret_cast<intptr_t>(promiseHolder))) {
-    delete promiseHolder;
+         reinterpret_cast<intptr_t>(promiseHolder.get()))) {
     return GenericPromise::CreateAndReject(NS_ERROR_FAILURE, __func__);
   }
+  RefPtr<GenericPromise> result = promiseHolder->Ensure(__func__);
   // promiseHolder will removed by receive message
-  return promiseHolder->Ensure(__func__);
+  mResponsePromises.AppendElement(Move(promiseHolder));
+  return Move(result);
 }
 
 mozilla::ipc::IPCResult
 RemoteSpellcheckEngineChild::RecvNotifyOfCurrentDictionary(
                                const nsString& aDictionary,
                                const intptr_t& aId)
 {
   MozPromiseHolder<GenericPromise>* promiseHolder =
     reinterpret_cast<MozPromiseHolder<GenericPromise>*>(aId);
   mOwner->mCurrentDictionary = aDictionary;
   if (aDictionary.IsEmpty()) {
     promiseHolder->RejectIfExists(NS_ERROR_NOT_AVAILABLE, __func__);
   } else {
     promiseHolder->ResolveIfExists(true, __func__);
   }
-  delete promiseHolder;
+  for (uint32_t i = 0; i < mResponsePromises.Length(); ++i) {
+    if (mResponsePromises[i].get() == promiseHolder) {
+      mResponsePromises.RemoveElementAt(i);
+      break;
+    }
+  }
   return IPC_OK();
 }
 
 } //namespace mozilla

--- a/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineChild.h
+++ b/extensions/spellcheck/hunspell/glue/RemoteSpellCheckEngineChild.h
@@ -23,13 +23,14 @@ public:
                                     const nsString& aDictionary,
                                     const intptr_t& aPromiseId) override;
 
   RefPtr<GenericPromise> SetCurrentDictionaryFromList(
                            const nsTArray<nsString>& aList);
 
 private:
   mozSpellChecker *mOwner;
+  nsTArray<UniquePtr<MozPromiseHolder<GenericPromise>>> mResponsePromises;
 };
 
 } //namespace mozilla
 
 #endif // RemoteSpellcheckEngineChild_h_