diff --git a/uriloader/exthandler/nsExternalHelperAppService.cpp b/uriloader/exthandler/nsExternalHelperAppService.cpp
index 02a555f04c..dc7d200041 100644
--- a/uriloader/exthandler/nsExternalHelperAppService.cpp
+++ b/uriloader/exthandler/nsExternalHelperAppService.cpp
@@ -384,6 +384,9 @@ static const nsDefaultMimeTypeEntry defaultMimeEntries[] =
   { "application/xhtml+xml", "xhtml" },
   { "application/xhtml+xml", "xht" },
   { TEXT_PLAIN, "txt" },
+  { APPLICATION_JSON, "json"},
+  { APPLICATION_XJAVASCRIPT, "js"},
+  { APPLICATION_XJAVASCRIPT, "jsm"},
   { VIDEO_OGG, "ogv" },
   { VIDEO_OGG, "ogg" },
   { APPLICATION_OGG, "ogg" },