diff --git a/calendar/base/content/preferences/connection.js b/calendar/base/content/preferences/connection.js

--- a/calendar/base/content/preferences/connection.js

+++ b/calendar/base/content/preferences/connection.js

@@ -69,17 +69,22 @@ var gConnectionsDialog = {

       }

     }

     var noProxiesPref = document.getElementById("network.proxy.no_proxies_on");

     noProxiesPref.value = noProxiesPref.value.replace(/[;]/g,',');

     return true;

   },

-  

+ 

+  checkForSystemProxy: function ()

+  {

+    if ("@mozilla.org/system-proxy-settings;1" in Components.classes)

+      document.getElementById("systemPref").removeAttribute("hidden");

+  },

   /**

    * Handler function to be called when the network.proxy.type preference has

    * changed while the connection preferences dialog is open.

    */

   proxyTypeChanged: function gCD_proxyTypeChanged() {

     var proxyTypePref = document.getElementById("network.proxy.type");

diff --git a/calendar/base/content/preferences/connection.xul b/calendar/base/content/preferences/connection.xul

--- a/calendar/base/content/preferences/connection.xul

+++ b/calendar/base/content/preferences/connection.xul

@@ -40,16 +40,17 @@

 <?xml-stylesheet href="chrome://global/skin/"?>

 <prefwindow id="ConnectionsDialog" type="child"

             xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"

             title="&connectionsDialog.title;"

             dlgbuttons="accept,cancel"

             onbeforeaccept="return gConnectionsDialog.beforeAccept();"

+            onload="gConnectionsDialog.checkForSystemProxy();"

 #ifdef XP_MACOSX

             style="width: &window.macWidth; !important;">

 #else

             style="width: &window.width; !important;">

 #endif

   <prefpane id="ConnectionsDialogPane">

@@ -88,16 +89,17 @@

     <groupbox>

       <caption label="&proxyTitle.label;"/>

       <radiogroup id="networkProxyType" preference="network.proxy.type"

                   onsyncfrompreference="return gConnectionsDialog.readProxyType();">

         <radio value="0" label="&directTypeRadio.label;" accesskey="&directTypeRadio.accesskey;"/>

         <radio value="4" label="&WPADTypeRadio.label;" accesskey="&WPADTypeRadio.accesskey;"/>

+        <radio value="5" label="&systemTypeRadio.label;" accesskey="&systemTypeRadio.accesskey;" id="systemPref" hidden="true"/>

         <radio value="1" label="&manualTypeRadio.label;" accesskey="&manualTypeRadio.accesskey;"/>

         <grid class="indent" flex="1">

           <columns>

             <column/>

             <column flex="1"/>

           </columns>

           <rows>

             <row align="center">

diff --git a/calendar/locales/en-US/chrome/calendar/preferences/connection.dtd b/calendar/locales/en-US/chrome/calendar/preferences/connection.dtd

--- a/calendar/locales/en-US/chrome/calendar/preferences/connection.dtd

+++ b/calendar/locales/en-US/chrome/calendar/preferences/connection.dtd

@@ -43,16 +43,18 @@

 <!ENTITY  window.width                  "37em">

 <!ENTITY  window.macWidth               "39em">

 <!ENTITY  proxyTitle.label              "Configure Proxies to Access the Internet">

 <!ENTITY  directTypeRadio.label         "Direct connection to the Internet">

 <!ENTITY  directTypeRadio.accesskey     "d">

 <!ENTITY  WPADTypeRadio.label           "Auto-detect proxy settings for this network">

 <!ENTITY  WPADTypeRadio.accesskey       "w">

+<!ENTITY  systemTypeRadio.label         "Use system proxy settings">

+<!ENTITY  systemTypeRadio.accesskey     "u">

 <!ENTITY  manualTypeRadio.label         "Manual proxy configuration:">

 <!ENTITY  manualTypeRadio.accesskey     "m">

 <!ENTITY  autoTypeRadio.label           "Automatic proxy configuration URL:">

 <!ENTITY  autoTypeRadio.accesskey       "A">

 <!ENTITY  reload.label                  "Reload">

 <!ENTITY  reload.accesskey              "e">

 <!ENTITY  ftp.label                     "FTP Proxy:">

 <!ENTITY  ftp.accesskey                 "F">