--- a/toolkit/mozapps/extensions/content/newaddon.xul
+++ b/toolkit/mozapps/extensions/content/newaddon.xul
@@ -47,20 +47,21 @@
       <checkbox id="allow" label="&allow;"/>
       <description id="later">&later;</description>
 
       <deck id="buttonDeck">
         <hbox id="continuePanel">
           <button id="continue-button" label="&continue;"
                   oncommand="continueClicked()"/>
         </hbox>
-        <hbox id="restartPanel">
-          <spacer id="restartSpacer"/>
-          <description id="restartMessage" flex="1">&restartMessage;</description>
-          <button id="restart-button" label="&restartButton;" oncommand="restartClicked()"/>
-          <button id="cancel-button" label="&cancelButton;" oncommand="cancelClicked()"/>
-        </hbox>
+        <vbox id="restartPanel">
+          <description id="restartMessage">&restartMessage;</description>
+          <hbox id="restartPanelButtons">
+            <button id="restart-button" label="&restartButton;" oncommand="restartClicked()"/>
+            <button id="cancel-button" label="&cancelButton;" oncommand="cancelClicked()"/>
+          </hbox>
+        </vbox>
       </deck>
     </vbox>
 
     <spacer id="spacer-end"/>
   </scrollbox>
 </page>

--- a/toolkit/themes/shared/extensions/newaddon.inc.css
+++ b/toolkit/themes/shared/extensions/newaddon.inc.css
@@ -84,30 +84,32 @@
   -moz-margin-end: 5px;
 }
 
 #allow {
   -moz-margin-start: 84px;
   margin-bottom: 20px;
 }
 
-#continuePanel,
-#restartPanel {
+#buttonDeck {
   margin-top: 25px;
-  -moz-box-pack: end;
-  -moz-box-align: center;
+  -moz-box-align: stretch;
+  -moz-box-pack: stretch;
 }
 
 #continuePanel {
   -moz-box-pack: end;
+  -moz-box-align: end;
 }
 
-#restartMessage {
-  text-align: right;
+#restartPanel {
+  -moz-box-pack: end;
+  -moz-box-align: stretch;
 }
 
-#restartSpacer {
-  -moz-box-flex: 1;
+#restartPanelButtons {
+  margin-top: 25px;
+  -moz-box-pack: end;
 }
 
 #later {
   color: GrayText;
 }