diff --git a/mozilla/mail/components/preferences/downloadactions.js b/mozilla/mail/components/preferences/downloadactions.js
index d4318840d24..003bc22d5f0 100644
--- a/mozilla/mail/components/preferences/downloadactions.js
+++ b/mozilla/mail/components/preferences/downloadactions.js
@@ -298,6 +298,8 @@ var gDownloadActionsWindow = {
       catch (e) {
         customHandler = null;
       }      
+      if (customHandler && !customHandler.exists())
+        customHandler = null;
       var mimeType = this._getLiteralValue(type, "value");
       var typeInfo = this._mimeSvc.getFromTypeAndExtension(mimeType, null);