diff --git a/uriloader/exthandler/nsExternalHelperAppService.cpp b/uriloader/exthandler/nsExternalHelperAppService.cpp
index a38695d3fac6..21a9535460dc 100644
--- a/uriloader/exthandler/nsExternalHelperAppService.cpp
+++ b/uriloader/exthandler/nsExternalHelperAppService.cpp
@@ -157,6 +157,7 @@ static const char* const nonDecodableTypes [] = {
 static const char* const nonDecodableExtensions [] = {
   "gz",
   "zip",
+  "Z",
   0
 };