diff --git a/extensions/firefox/content/PdfJs.jsm b/extensions/firefox/content/PdfJs.jsm
index 54cbf5812..d360cda69 100644
--- a/extensions/firefox/content/PdfJs.jsm
+++ b/extensions/firefox/content/PdfJs.jsm
@@ -192,6 +192,7 @@ let PdfJs = {
     var handlerInfo = Svc.mime.
                         getFromTypeAndExtension('application/pdf', 'pdf');
     return handlerInfo.alwaysAskBeforeHandling == false &&
+           handlerInfo.plugin == null &&
            handlerInfo.preferredAction == Ci.nsIHandlerInfo.handleInternally;
   },