diff --git a/extensions/firefox/content/PdfJs.jsm b/extensions/firefox/content/PdfJs.jsm
index 5522312d6..079e3a39e 100644
--- a/extensions/firefox/content/PdfJs.jsm
+++ b/extensions/firefox/content/PdfJs.jsm
@@ -254,7 +254,7 @@ let PdfJs = {
     this._pdfStreamConverterFactory.unregister();
     delete this._pdfStreamConverterFactory;
 
-    this._pdfRedirectorFactory.unregister;
+    this._pdfRedirectorFactory.unregister();
     delete this._pdfRedirectorFactory;
     Svc.pluginHost.unregisterPlayPreviewMimeType(PDF_CONTENT_TYPE);