bump version for Firefox 23

Change-Id: I5a61570faae3977dea0f2ad31ca2d08471bd2ba7
diff --git a/MissingPlugin/war/MissingPlugin.html b/MissingPlugin/war/MissingPlugin.html
index a426ec1..34dcc5a 100644
--- a/MissingPlugin/war/MissingPlugin.html
+++ b/MissingPlugin/war/MissingPlugin.html
@@ -35,7 +35,7 @@
 
           "firefox-old" :
           {
-            "caption" : "Sorry, the GWT Developer Plugin only supports Firefox 3.0 - 22.0 at present",
+            "caption" : "Sorry, the GWT Developer Plugin only supports Firefox 3.0 - 23.0 at present",
             "url" : "http://www.getfirefox.com",
             "supported" : false
           },
@@ -173,7 +173,7 @@
       } else if (ua.indexOf("gecko") != -1) {
         // Note: Gecko version != Firefox version before 5.0.
         // See: https://developer.mozilla.org/en-US/docs/Gecko_user_agent_string_reference
-        var gecko_versions = ["1.9", "2.0", "5.0", "6.0", "7.0", "8.0", "9.0", "10.0", "11.0", "12.0", "13.0", "14.0", "15.0", "16.0", "17.0", "18.0", "19.0", "20.0", "21.0", "22.0"];
+        var gecko_versions = ["1.9", "2.0", "5.0", "6.0", "7.0", "8.0", "9.0", "10.0", "11.0", "12.0", "13.0", "14.0", "15.0", "16.0", "17.0", "18.0", "19.0", "20.0", "21.0", "22.0", "23.0"];
         id = 'firefox-old';
         for (var i = 0; i < gecko_versions.length; i++) {
           if (ua.indexOf("rv:" + gecko_versions[i]) != -1) {