diff -r 000000000000 -r 6474c204b198 toolkit/devtools/webconsole/test/unit/test_network_helper.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/devtools/webconsole/test/unit/test_network_helper.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,47 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+const Cu = Components.utils;
+const { devtools } = Cu.import("resource://gre/modules/devtools/Loader.jsm", {});
+
+Object.defineProperty(this, "NetworkHelper", {
+  get: function() {
+    return devtools.require("devtools/toolkit/webconsole/network-helper");
+  },
+  configurable: true,
+  writeable: false,
+  enumerable: true
+});
+
+function run_test() {
+  test_isTextMimeType();
+}
+
+function test_isTextMimeType () {
+  do_check_eq(NetworkHelper.isTextMimeType("text/plain"), true);
+  do_check_eq(NetworkHelper.isTextMimeType("application/javascript"), true);
+  do_check_eq(NetworkHelper.isTextMimeType("application/json"), true);
+  do_check_eq(NetworkHelper.isTextMimeType("text/css"), true);
+  do_check_eq(NetworkHelper.isTextMimeType("text/html"), true);
+  do_check_eq(NetworkHelper.isTextMimeType("image/svg+xml"), true);
+  do_check_eq(NetworkHelper.isTextMimeType("application/xml"), true);
+
+  // Test custom JSON subtype
+  do_check_eq(NetworkHelper.isTextMimeType("application/vnd.tent.posts-feed.v0+json"), true);
+  do_check_eq(NetworkHelper.isTextMimeType("application/vnd.tent.posts-feed.v0-json"), true);
+  // Test custom XML subtype
+  do_check_eq(NetworkHelper.isTextMimeType("application/vnd.tent.posts-feed.v0+xml"), true);
+  do_check_eq(NetworkHelper.isTextMimeType("application/vnd.tent.posts-feed.v0-xml"), false);
+  // Test case-insensitive
+  do_check_eq(NetworkHelper.isTextMimeType("application/vnd.BIG-CORP+json"), true);
+  // Test non-text type
+  do_check_eq(NetworkHelper.isTextMimeType("image/png"), false);
+  // Test invalid types
+  do_check_eq(NetworkHelper.isTextMimeType("application/foo-+json"), false);
+  do_check_eq(NetworkHelper.isTextMimeType("application/-foo+json"), false);
+  do_check_eq(NetworkHelper.isTextMimeType("application/foo--bar+json"), false);
+
+  // Test we do not cause internal errors with unoptimized regex. Bug 961097
+  do_check_eq(NetworkHelper.isTextMimeType("application/vnd.google.safebrowsing-chunk"), false);
+}