diff -u -r mozilla/layout/base/nsPresContext.cpp mozilla.thunderbird/layout/base/nsPresContext.cpp
--- mozilla/layout/base/nsPresContext.cpp	2006-04-21 19:30:50.000000000 -0400
+++ mozilla.thunderbird/layout/base/nsPresContext.cpp	2007-08-17 15:29:36.000000000 -0400
@@ -68,6 +68,7 @@
 #include "nsIWeakReferenceUtils.h"
 #include "nsCSSRendering.h"
 #include "prprf.h"
+#include "prnetdb.h"
 #include "nsContentPolicyUtils.h"
 #include "nsIScriptGlobalObject.h"
 #include "nsIDOMDocument.h"
@@ -258,6 +259,14 @@
   nsContentUtils::UnregisterPrefCallback("image.animation_mode",
                                          nsPresContext::PrefChangedCallback,
                                          this);
+  nsContentUtils::UnregisterPrefCallback("image.animation_mode", 
+                                         nsPresContext::PrefChangedCallback,
+                                         this);
+#ifdef MOZ_DNSSEC
+  nsContentUtils::UnregisterPrefCallback("security.dnssec.dnssecBehavior",
+                                         nsPresContext::PrefChangedCallback,
+                                         this);
+#endif
 #ifdef IBMBIDI
   nsContentUtils::UnregisterPrefCallback("bidi.", PrefChangedCallback, this);
 
@@ -571,6 +580,10 @@
   else if (animatePref.Equals("once"))
     mImageAnimationModePref = imgIContainer::kLoopOnceAnimMode;
 
+#ifdef MOZ_DNSSEC
+  PR_set_dnssec_validate_policy(nsContentUtils::GetIntPref("security.dnssec.dnssecBehavior"));
+#endif /* MOZ_DNSSEC */
+
 #ifdef IBMBIDI
   PRInt32 prefInt =
     nsContentUtils::GetIntPref("bidi.direction",
@@ -704,6 +717,11 @@
   nsContentUtils::RegisterPrefCallback("image.animation_mode",
                                        nsPresContext::PrefChangedCallback,
                                        this);
+#ifdef MOZ_DNSSEC
+  nsContentUtils::RegisterPrefCallback("security.dnssec.dnssecBehavior",
+                                       nsPresContext::PrefChangedCallback,
+                                       this);
+#endif
 #ifdef IBMBIDI
   nsContentUtils::RegisterPrefCallback("bidi.", PrefChangedCallback,
                                        this);
diff -u -r mozilla/mail/components/preferences/privacy.xul mozilla.thunderbird/mail/components/preferences/privacy.xul
--- mozilla/mail/components/preferences/privacy.xul	2005-10-04 20:12:50.000000000 -0400
+++ mozilla.thunderbird/mail/components/preferences/privacy.xul	2007-08-23 11:50:57.000000000 -0400
@@ -88,6 +88,9 @@
       <preference id="security.disable_button.openDeviceManager"
                   name="security.disable_button.openDeviceManager"
                   type="bool"/>
+      <preference id="security.dnssec.dnssecBehavior"
+                  name="security.dnssec.dnssecBehavior"
+                  type="int"/>                   
     </preferences>
 
     <tabbox id="privacyPrefs" flex="1" onselect="gPrivacyPane.tabSelectionChanged();">
@@ -97,6 +100,7 @@
         <tab label="&itemAntiVirus.label;"/>
         <tab label="&itemPasswords.label;"/>
         <tab label="&itemSecurity.label;"/>
+        <tab label="&dnssecTab.label;"/>
       </tabs>
       
       <tabpanels flex="1">
@@ -188,6 +192,19 @@
                     preference="security.disable_button.openDeviceManager"/>
           </description>
         </tabpanel>
+        <!-- DNS Security --> 
+        <tabpanel orient="vertical">
+          <description>&dnssec.description;</description>
+          <separator class="thin"/>
+          <groupbox>
+            <radiogroup id="networkDnssecBehaviour" preference="security.dnssec.dnssecBehavior">
+                <radio value="1" label="&neverDNSSecure.label;"
+                       accesskey="&neverDNSSecure.accesskey;"/>
+                <radio value="0" label="&possibleDNSSecure.label;"
+                       accesskey="&possibleDNSSecure.accesskey;"/>
+            </radiogroup>
+          </groupbox>
+        </tabpanel>
       </tabpanels>
     </tabbox>
 
diff -u -r mozilla/mail/locales/en-US/chrome/messenger/preferences/privacy.dtd mozilla.thunderbird/mail/locales/en-US/chrome/messenger/preferences/privacy.dtd
--- mozilla/mail/locales/en-US/chrome/messenger/preferences/privacy.dtd	2005-04-05 19:29:32.000000000 -0400
+++ mozilla.thunderbird/mail/locales/en-US/chrome/messenger/preferences/privacy.dtd	2007-08-23 11:52:45.000000000 -0400
@@ -40,6 +40,17 @@
 <!ENTITY viewSecurityDevices.label      "Security Devices">
 <!ENTITY viewSecurityDevices.accesskey  "u">
 
+<!-- DNS Security -->
+<!ENTITY dnssecTab.label                "DNS Security">
+<!ENTITY dnssec.description             "DNS Security Policy is currently set at the system level (/etc/dnsval.conf) and this option allows that policy to be enforced or ignored.">
+<!ENTITY dnsSecurity.label              "DNS Security Policy">
+<!ENTITY neverDNSSecure.label           "Ignore DNS security">
+<!ENTITY neverDNSSecure.accesskey       "N">
+<!ENTITY possibleDNSSecure.label        "Enforce DNS Security">
+<!ENTITY possibleDNSSecure.accesskey    "E">
+<!ENTITY allDNSSecure.label             "Require all DNS lookups to be secure">
+<!ENTITY allDNSSecure.accesskey         "A">
+
 <!-- Anti Virus -->
 <!ENTITY antiVirus.intro      "&brandShortName; can make it easy for anti-virus software to analyze incoming mail messages for viruses before they are stored locally.">
 <!ENTITY antiVirus.label      "Allow anti-virus clients to quarantine individual incoming messages">