diff --git a/toolkit/components/autocomplete/nsAutoCompleteController.cpp b/toolkit/components/autocomplete/nsAutoCompleteController.cpp
index 42dc709cac89..3d4d70ab910b 100644
--- a/toolkit/components/autocomplete/nsAutoCompleteController.cpp
+++ b/toolkit/components/autocomplete/nsAutoCompleteController.cpp
@@ -71,7 +71,7 @@ nsAutoCompleteController::nsAutoCompleteController() :
   mRowCount(0),
   mSearchesOngoing(0),
   mSearchesFailed(0),
-  mFirstSearchResult(false),
+  mDelayedRowCountDelta(0),
   mImmediateSearchesCount(0),
   mCompletedSelectionIndex(-1)
 {
@@ -216,6 +216,7 @@ nsAutoCompleteController::ResetInternalState()
   mProhibitAutoFill = false;
   mSearchStatus = nsIAutoCompleteController::STATUS_NONE;
   mRowCount = 0;
+  mDelayedRowCountDelta = 0;
   mCompletedSelectionIndex = -1;
 
   return NS_OK;
@@ -871,26 +872,15 @@ nsAutoCompleteController::HandleSearchResult(nsIAutoCompleteSearch *aSearch,
 ////////////////////////////////////////////////////////////////////////
 //// nsIAutoCompleteObserver
 
-NS_IMETHODIMP
-nsAutoCompleteController::OnUpdateSearchResult(nsIAutoCompleteSearch *aSearch, nsIAutoCompleteResult* aResult)
-{
-  MOZ_ASSERT(mSearches.Contains(aSearch));
-
-  ClearResults();
-  HandleSearchResult(aSearch, aResult);
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 nsAutoCompleteController::OnSearchResult(nsIAutoCompleteSearch *aSearch, nsIAutoCompleteResult* aResult)
 {
   MOZ_ASSERT(mSearchesOngoing > 0 && mSearches.Contains(aSearch));
 
-  // If this is the first search result we are processing
-  // we should clear out the previously cached results.
-  if (mFirstSearchResult) {
-    ClearResults();
-    mFirstSearchResult = false;
+  // Update the tree if necessary.
+  if (mTree && mDelayedRowCountDelta != 0) {
+    mTree->RowCountChanged(0, mDelayedRowCountDelta);
+    mDelayedRowCountDelta = 0;
   }
 
   uint16_t result = 0;
@@ -1220,16 +1210,18 @@ nsAutoCompleteController::BeforeSearches()
   mSearchStatus = nsIAutoCompleteController::STATUS_SEARCHING;
   mDefaultIndexCompleted = false;
 
-  // The first search result will clear mResults array, though we should pass
-  // the previous result to each search to allow them to reuse it.  So we
-  // temporarily cache current results till AfterSearches().
+  // ClearResults will clear the mResults array, but we should pass the previous
+  // result to each search to allow reusing it.  So we temporarily cache the
+  // current results until AfterSearches().
   if (!mResultCache.AppendObjects(mResults)) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
-
+  // The rowCountChanged notification is sent later, when the first result
+  // from the search arrives, to avoid flickering in the tree contents.
+  mDelayedRowCountDelta = 0;
+  ClearResults(true);
   mSearchesOngoing = mSearches.Length();
   mSearchesFailed = 0;
-  mFirstSearchResult = true;
 
   // notify the input that the search is beginning
   mInput->OnSearchBegin();
@@ -1731,6 +1723,12 @@ nsAutoCompleteController::PostSearchCleanup()
   uint32_t minResults;
   input->GetMinResultsForPopup(&minResults);
 
+  // Apply a pending rowCountChanged.
+  if (mTree && mDelayedRowCountDelta != 0) {
+    mTree->RowCountChanged(0, mDelayedRowCountDelta);
+    // mDelayedRowCountDelta will be reset by the next search.
+  }
+
   if (mRowCount || minResults == 0) {
     OpenPopup();
     if (mRowCount)
@@ -1749,15 +1747,22 @@ nsAutoCompleteController::PostSearchCleanup()
 }
 
 nsresult
-nsAutoCompleteController::ClearResults()
+nsAutoCompleteController::ClearResults(bool aIsSearching)
 {
   int32_t oldRowCount = mRowCount;
   mRowCount = 0;
   mResults.Clear();
   if (oldRowCount != 0) {
-    if (mTree)
-      mTree->RowCountChanged(0, -oldRowCount);
-    else if (mInput) {
+    if (mTree) {
+      if (aIsSearching) {
+        // Delay the notification, so the tree provides a smoother transition to
+        // the new result. It will be handled as soon as we add the first result.
+        mDelayedRowCountDelta = -oldRowCount;
+      } else {
+        // Notify immediately.
+        mTree->RowCountChanged(0, -oldRowCount);
+      }
+    } else if (mInput) {
       nsCOMPtr<nsIAutoCompletePopup> popup;
       mInput->GetPopup(getter_AddRefs(popup));
       NS_ENSURE_TRUE(popup != nullptr, NS_ERROR_FAILURE);
diff --git a/toolkit/components/autocomplete/nsAutoCompleteController.h b/toolkit/components/autocomplete/nsAutoCompleteController.h
index f43c63d3c3f4..0c2cc8b30c3d 100644
--- a/toolkit/components/autocomplete/nsAutoCompleteController.h
+++ b/toolkit/components/autocomplete/nsAutoCompleteController.h
@@ -117,7 +117,7 @@ protected:
    */
   nsresult GetFinalDefaultCompleteValue(nsAString &_retval);
 
-  nsresult ClearResults();
+  nsresult ClearResults(bool aIsSearching = false);
 
   nsresult RowIndexToSearch(int32_t aRowIndex,
                             int32_t *aSearchIndex, int32_t *aItemIndex);
@@ -164,7 +164,7 @@ protected:
   uint32_t mRowCount;
   uint32_t mSearchesOngoing;
   uint32_t mSearchesFailed;
-  bool mFirstSearchResult;
+  int32_t mDelayedRowCountDelta;
   uint32_t mImmediateSearchesCount;
   // The index of the match on the popup that was selected using the keyboard,
   // if the completeselectedindex attribute is set.
diff --git a/toolkit/components/autocomplete/nsIAutoCompleteSearch.idl b/toolkit/components/autocomplete/nsIAutoCompleteSearch.idl
index 188c333ac687..e7f828436f2a 100644
--- a/toolkit/components/autocomplete/nsIAutoCompleteSearch.idl
+++ b/toolkit/components/autocomplete/nsIAutoCompleteSearch.idl
@@ -40,14 +40,6 @@ interface nsIAutoCompleteObserver : nsISupports
    * @param result - The search result object
    */
   void onSearchResult(in nsIAutoCompleteSearch search, in nsIAutoCompleteResult result);
-
-  /*
-   * Called to update with new results
-   *
-   * @param search - The search object that processed this search
-   * @param result - The search result object
-   */
-  void onUpdateSearchResult(in nsIAutoCompleteSearch search, in nsIAutoCompleteResult result);
 };
 
 [scriptable, uuid(4c3e7462-fbfb-4310-8f4b-239238392b75)]
diff --git a/toolkit/components/places/UnifiedComplete.js b/toolkit/components/places/UnifiedComplete.js
index 188a3b054962..eae2fdc98803 100644
--- a/toolkit/components/places/UnifiedComplete.js
+++ b/toolkit/components/places/UnifiedComplete.js
@@ -2384,6 +2384,8 @@ Search.prototype = {
   _notifyDelaysCount: 0,
   notifyResult(searchOngoing, skipDelay = false) {
     let notify = () => {
+      if (!this.pending)
+        return;
       this._notifyDelaysCount = 0;
       let resultCode = this._currentMatchCount ? "RESULT_SUCCESS" : "RESULT_NOMATCH";
       if (searchOngoing) {