diff --git a/mail/installer/windows/nsis/installer.nsi b/mail/installer/windows/nsis/installer.nsi
index 66f4a0e0bd..ec53074211 100755
--- a/mail/installer/windows/nsis/installer.nsi
+++ b/mail/installer/windows/nsis/installer.nsi
@@ -217,6 +217,15 @@ Section "-InstallStartCleanup"
     ClearErrors
   ${EndIf}
 
+  ; Delete two files installed by Kaspersky Anti-Spam extension that are only
+  ; compatible with Thunderbird 2 (bug 533692).
+  ${If} ${FileExists} "$INSTDIR\components\klthbplg.dll"
+    Delete /REBOOTOK "$INSTDIR\components\klthbplg.dll"
+  ${EndIf}
+  ${If} ${FileExists} "$INSTDIR\components\IKLAntiSpam.xpt"
+    Delete /REBOOTOK "$INSTDIR\components\IKLAntiSpam.xpt"
+  ${EndIf}
+
   ; Remove the updates directory for Vista and above
   ${CleanUpdatesDir} "Thunderbird"
 
diff --git a/mail/installer/windows/nsis/shared.nsh b/mail/installer/windows/nsis/shared.nsh
index ce7289e4ae..46c808f3e9 100755
--- a/mail/installer/windows/nsis/shared.nsh
+++ b/mail/installer/windows/nsis/shared.nsh
@@ -49,6 +49,15 @@
   ; Upgrade the copies of the MAPI DLL's
   ${UpgradeMapiDLLs}
 
+  ; Delete two files installed by Kaspersky Anti-Spam extension that are only
+  ; compatible with Thunderbird 2 (bug 533692).
+  ${If} ${FileExists} "$INSTDIR\components\klthbplg.dll"
+    Delete /REBOOTOK "$INSTDIR\components\klthbplg.dll"
+  ${EndIf}
+  ${If} ${FileExists} "$INSTDIR\components\IKLAntiSpam.xpt"
+    Delete /REBOOTOK "$INSTDIR\components\IKLAntiSpam.xpt"
+  ${EndIf}
+
   ClearErrors
   WriteRegStr HKLM "Software\Mozilla" "${BrandShortName}InstallerTest" "Write Test"
   ${If} ${Errors}