diff -up thunderbird-60.2.1/comm/ldap/xpcom/public/nsILDAPOperation.idl.1460871-ldap-query thunderbird-60.2.1/comm/ldap/xpcom/public/nsILDAPOperation.idl
--- thunderbird-60.2.1/comm/ldap/xpcom/public/nsILDAPOperation.idl.1460871-ldap-query	2018-10-01 16:52:39.000000000 +0200
+++ thunderbird-60.2.1/comm/ldap/xpcom/public/nsILDAPOperation.idl	2018-10-04 09:40:04.491575949 +0200
@@ -52,6 +52,10 @@ interface nsILDAPOperation : nsISupports
      * private parameter (anything caller desires)
      */
     attribute nsISupports closure;
+    /**
+     * number of the request for compare that the request is still valid.
+     */
+    attribute unsigned long requestNum;
 
     /**
      * No time and/or size limit specified
diff -up thunderbird-60.2.1/comm/ldap/xpcom/src/nsLDAPOperation.cpp.1460871-ldap-query thunderbird-60.2.1/comm/ldap/xpcom/src/nsLDAPOperation.cpp
--- thunderbird-60.2.1/comm/ldap/xpcom/src/nsLDAPOperation.cpp.1460871-ldap-query	2018-10-01 16:52:39.000000000 +0200
+++ thunderbird-60.2.1/comm/ldap/xpcom/src/nsLDAPOperation.cpp	2018-10-04 09:40:04.491575949 +0200
@@ -400,6 +400,19 @@ convertControlArray(nsIArray *aXpcomArra
     return NS_OK;
 }
 
+  /* attribute unsigned long requestNum; */
+NS_IMETHODIMP nsLDAPOperation::GetRequestNum(uint32_t *aRequestNum)
+{
+    *aRequestNum = mRequestNum;
+    return NS_OK;
+}
+
+NS_IMETHODIMP nsLDAPOperation::SetRequestNum(uint32_t aRequestNum)
+{
+    mRequestNum = aRequestNum;
+    return NS_OK;
+}
+
 NS_IMETHODIMP
 nsLDAPOperation::SearchExt(const nsACString& aBaseDn, int32_t aScope,
                            const nsACString& aFilter,
diff -up thunderbird-60.2.1/comm/ldap/xpcom/src/nsLDAPOperation.h.1460871-ldap-query thunderbird-60.2.1/comm/ldap/xpcom/src/nsLDAPOperation.h
--- thunderbird-60.2.1/comm/ldap/xpcom/src/nsLDAPOperation.h.1460871-ldap-query	2018-10-01 16:52:39.000000000 +0200
+++ thunderbird-60.2.1/comm/ldap/xpcom/src/nsLDAPOperation.h	2018-10-04 09:40:04.491575949 +0200
@@ -36,6 +36,8 @@ class nsLDAPOperation : public nsILDAPOp
      * used to break cycles
      */
     void Clear();
+    // Stores the request number for later check of the operation is still valid
+    int32_t mRequestNum;
 
   private:
     virtual ~nsLDAPOperation();
diff -up thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPDirectoryQuery.cpp.1460871-ldap-query thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPDirectoryQuery.cpp
--- thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPDirectoryQuery.cpp.1460871-ldap-query	2018-10-01 16:52:43.000000000 +0200
+++ thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPDirectoryQuery.cpp	2018-10-04 09:40:55.334670404 +0200
@@ -22,6 +22,8 @@
 
 using namespace mozilla;
 
+extern mozilla::LazyLogModule gLDAPLogModule; // defined in nsLDAPService.cpp
+
 // nsAbLDAPListenerBase inherits nsILDAPMessageListener
 class nsAbQueryLDAPMessageListener : public nsAbLDAPListenerBase
 {
@@ -66,7 +68,6 @@ protected:
 
   bool mFinished;
   bool mCanceled;
-  bool mWaitingForPrevQueryToFinish;
 
   nsCOMPtr<nsIMutableArray> mServerSearchControls;
   nsCOMPtr<nsIMutableArray> mClientSearchControls;
@@ -94,7 +95,6 @@ nsAbQueryLDAPMessageListener::nsAbQueryL
   mResultLimit(resultLimit),
   mFinished(false),
   mCanceled(false),
-  mWaitingForPrevQueryToFinish(false),
   mServerSearchControls(serverSearchControls),
   mClientSearchControls(clientSearchControls)
 {
@@ -116,9 +116,6 @@ nsresult nsAbQueryLDAPMessageListener::C
         return NS_OK;
 
     mCanceled = true;
-    if (!mFinished)
-      mWaitingForPrevQueryToFinish = true;
-
     return NS_OK;
 }
 
@@ -129,6 +126,8 @@ NS_IMETHODIMP nsAbQueryLDAPMessageListen
 
   int32_t messageType;
   rv = aMessage->GetType(&messageType);
+  uint32_t requestNum;
+  mOperation->GetRequestNum(&requestNum);
   NS_ENSURE_SUCCESS(rv, rv);
 
   bool cancelOperation = false;
@@ -137,6 +136,14 @@ NS_IMETHODIMP nsAbQueryLDAPMessageListen
   {
     MutexAutoLock lock (mLock);
 
+    if (requestNum != sCurrentRequestNum) {
+      MOZ_LOG(gLDAPLogModule, mozilla::LogLevel::Debug,
+           ("nsAbQueryLDAPMessageListener::OnLDAPMessage: Ignoring message with "
+            "request num %d, current request num is %d.",
+            requestNum, sCurrentRequestNum));
+      return NS_OK;
+    }
+
     if (mFinished)
       return NS_OK;
 
@@ -166,11 +173,10 @@ NS_IMETHODIMP nsAbQueryLDAPMessageListen
         rv = OnLDAPMessageSearchResult(aMessage);
       break;
     case nsILDAPMessage::RES_SEARCH_ENTRY:
-      if (!mFinished && !mWaitingForPrevQueryToFinish)
+      if (!mFinished)
         rv = OnLDAPMessageSearchEntry(aMessage);
       break;
     case nsILDAPMessage::RES_SEARCH_RESULT:
-      mWaitingForPrevQueryToFinish = false;
       rv = OnLDAPMessageSearchResult(aMessage);
       NS_ENSURE_SUCCESS(rv, rv);
       break;
@@ -207,6 +213,8 @@ nsresult nsAbQueryLDAPMessageListener::D
   rv = mOperation->Init(mConnection, this, nullptr);
   NS_ENSURE_SUCCESS(rv, rv);
 
+  mOperation->SetRequestNum(++sCurrentRequestNum);
+
   nsAutoCString dn;
   rv = mSearchUrl->GetDn(dn);
   NS_ENSURE_SUCCESS(rv, rv);
diff -up thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPListenerBase.cpp.1460871-ldap-query thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPListenerBase.cpp
--- thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPListenerBase.cpp.1460871-ldap-query	2018-10-01 16:52:43.000000000 +0200
+++ thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPListenerBase.cpp	2018-10-04 09:40:04.492575951 +0200
@@ -20,6 +20,8 @@
 
 using namespace mozilla;
 
+uint32_t nsAbLDAPListenerBase::sCurrentRequestNum = 0;
+
 nsAbLDAPListenerBase::nsAbLDAPListenerBase(nsILDAPURL* url,
                                            nsILDAPConnection* connection,
                                            const nsACString &login,
@@ -249,6 +251,7 @@ NS_IMETHODIMP nsAbLDAPListenerBase::OnLD
     InitFailed();
     return rv;
   }
+  mOperation->SetRequestNum(++sCurrentRequestNum);
 
   // Try non-password mechanisms first
   if (mSaslMechanism.EqualsLiteral("GSSAPI"))
diff -up thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPListenerBase.h.1460871-ldap-query thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPListenerBase.h
--- thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPListenerBase.h.1460871-ldap-query	2018-10-01 16:52:43.000000000 +0200
+++ thunderbird-60.2.1/comm/mailnews/addrbook/src/nsAbLDAPListenerBase.h	2018-10-04 09:40:04.492575951 +0200
@@ -47,6 +47,7 @@ protected:
   int32_t mTimeOut;
   bool mBound;
   bool mInitialized;
+  static uint32_t sCurrentRequestNum;
 
   mozilla::Mutex mLock;
 };