diff --git a/toolkit/components/url-classifier/Classifier.cpp b/toolkit/components/url-classifier/Classifier.cpp
index 9ce55a3b593d..00caa202ff50 100644
--- a/toolkit/components/url-classifier/Classifier.cpp
+++ b/toolkit/components/url-classifier/Classifier.cpp
@@ -174,7 +174,7 @@ nsresult Classifier::SetupPathNames() {
 }
 
 nsresult Classifier::CreateStoreDirectory() {
-  if (mIsClosed) {
+  if (ShouldAbort()) {
     return NS_OK;  // nothing to do, the classifier is done
   }
 
@@ -236,10 +236,8 @@ nsresult Classifier::Open(nsIFile& aCacheDirectory) {
 }
 
 void Classifier::Close() {
-  // Close will be called by PreShutdown, set |mUpdateInterrupted| here
-  // to abort an ongoing update if possible. It is important to note that
+  // Close will be called by PreShutdown, so it is important to note that
   // things put here should not affect an ongoing update thread.
-  mUpdateInterrupted = true;
   mIsClosed = true;
   DropStores();
 }
@@ -763,7 +761,7 @@ nsresult Classifier::ApplyUpdatesBackground(TableUpdateArray& aUpdates,
 
   nsresult rv;
 
-  // Check point 1: Copying files takes time so we check |mUpdateInterrupted|
+  // Check point 1: Copying files takes time so we check ShouldAbort()
   //                inside CopyInUseDirForUpdate().
   rv = CopyInUseDirForUpdate();  // i.e. mUpdatingDirectory will be setup.
   if (NS_FAILED(rv)) {
@@ -784,7 +782,7 @@ nsresult Classifier::ApplyUpdatesBackground(TableUpdateArray& aUpdates,
     nsAutoCString updateTable(update->TableName());
 
     // Check point 2: Processing downloaded data takes time.
-    if (mUpdateInterrupted) {
+    if (ShouldAbort()) {
       LOG(("Update is interrupted. Stop building new tables."));
       return NS_OK;
     }
@@ -814,7 +812,7 @@ nsresult Classifier::ApplyUpdatesBackground(TableUpdateArray& aUpdates,
 
 nsresult Classifier::ApplyUpdatesForeground(
     nsresult aBackgroundRv, const nsACString& aFailedTableName) {
-  if (mUpdateInterrupted) {
+  if (ShouldAbort()) {
     LOG(("Update is interrupted! Just remove update intermediaries."));
     RemoveUpdateIntermediaries();
     return NS_OK;
@@ -867,7 +865,7 @@ void Classifier::DropStores() {
 }
 
 nsresult Classifier::RegenActiveTables() {
-  if (mIsClosed) {
+  if (ShouldAbort()) {
     return NS_OK;  // nothing to do, the classifier is done
   }
 
@@ -1047,7 +1045,7 @@ nsresult Classifier::DumpFailedUpdate() {
 
 /**
  * This function copies the files one by one to the destination folder.
- * Before copying a file, it checks |mUpdateInterrupted| and returns
+ * Before copying a file, it checks ::ShouldAbort and returns
  * NS_ERROR_ABORT if the flag is set.
  */
 nsresult Classifier::CopyDirectoryInterruptible(nsCOMPtr<nsIFile>& aDestDir,
@@ -1060,7 +1058,7 @@ nsresult Classifier::CopyDirectoryInterruptible(nsCOMPtr<nsIFile>& aDestDir,
   nsCOMPtr<nsIFile> source;
   while (NS_SUCCEEDED(rv = entries->GetNextFile(getter_AddRefs(source))) &&
          source) {
-    if (mUpdateInterrupted) {
+    if (ShouldAbort()) {
       LOG(("Update is interrupted. Aborting the directory copy"));
       return NS_ERROR_ABORT;
     }
@@ -1104,6 +1102,9 @@ nsresult Classifier::CopyDirectoryInterruptible(nsCOMPtr<nsIFile>& aDestDir,
 
 nsresult Classifier::CopyInUseDirForUpdate() {
   LOG(("Copy in-use directory content for update."));
+  if (ShouldAbort()) {
+    return NS_ERROR_UC_UPDATE_SHUTDOWNING;
+  }
 
   // We copy everything from in-use directory to a temporary directory
   // for updating.
@@ -1195,7 +1196,7 @@ nsCString Classifier::GetProvider(const nsACString& aTableName) {
  */
 nsresult Classifier::UpdateHashStore(TableUpdateArray& aUpdates,
                                      const nsACString& aTable) {
-  if (nsUrlClassifierDBService::ShutdownHasStarted()) {
+  if (ShouldAbort()) {
     return NS_ERROR_UC_UPDATE_SHUTDOWNING;
   }
 
@@ -1297,7 +1298,7 @@ nsresult Classifier::UpdateTableV4(TableUpdateArray& aUpdates,
                                    const nsACString& aTable) {
   MOZ_ASSERT(!NS_IsMainThread(),
              "UpdateTableV4 must be called on the classifier worker thread.");
-  if (nsUrlClassifierDBService::ShutdownHasStarted()) {
+  if (ShouldAbort()) {
     return NS_ERROR_UC_UPDATE_SHUTDOWNING;
   }
 
@@ -1446,7 +1447,7 @@ RefPtr<LookupCache> Classifier::GetLookupCache(const nsACString& aTable,
   }
 
   // We don't want to create lookupcache when shutdown is already happening.
-  if (nsUrlClassifierDBService::ShutdownHasStarted()) {
+  if (ShouldAbort()) {
     return nullptr;
   }
 
@@ -1622,5 +1623,10 @@ nsresult Classifier::LoadMetadata(nsIFile* aDirectory, nsACString& aResult) {
   return rv;
 }
 
+bool Classifier::ShouldAbort() const {
+  return mIsClosed || nsUrlClassifierDBService::ShutdownHasStarted() ||
+         (mUpdateInterrupted && (NS_GetCurrentThread() == mUpdateThread));
+}
+
 }  // namespace safebrowsing
 }  // namespace mozilla
diff --git a/toolkit/components/url-classifier/Classifier.h b/toolkit/components/url-classifier/Classifier.h
index 6d6fcc348f04..1be929c3bea1 100644
--- a/toolkit/components/url-classifier/Classifier.h
+++ b/toolkit/components/url-classifier/Classifier.h
@@ -202,6 +202,9 @@ class Classifier {
   nsresult ApplyUpdatesForeground(nsresult aBackgroundRv,
                                   const nsACString& aFailedTableName);
 
+  // Used by worker thread and update thread to abort current operation.
+  bool ShouldAbort() const;
+
   // Root dir of the Local profile.
   nsCOMPtr<nsIFile> mCacheDirectory;
   // Main directory where to store the databases.
@@ -225,8 +228,12 @@ class Classifier {
   // The copy of mLookupCaches for update only.
   LookupCacheArray mNewLookupCaches;
 
+  // True when Reset() is called.
   bool mUpdateInterrupted;
 
+  // True once CLose() has been called
+  bool mIsClosed;
+
   nsCOMPtr<nsIThread> mUpdateThread;  // For async update.
 
   // Identical to mRootStoreDirectory but for update only because
@@ -234,8 +241,6 @@ class Classifier {
   // be accessed in CopyInUseDirForUpdate().
   // It will be initialized right before update on the worker thread.
   nsCOMPtr<nsIFile> mRootStoreDirectoryForUpdate;
-
-  bool mIsClosed;  // true once Close() has been called
 };
 
 }  // namespace safebrowsing