update warning message

apps/firefox/templates/firefox/unsupported-warning.html

@@ -13,7 +13,7 @@
     <div id="wrapper">
       <div id="details-header">
         <h1>{{ _('URGENT!') }}</h1>
-        <p>{{ _('Your version of Firefox is no longer protected against online attacks.') }}</p>
+        <p>{{ _('Your version of Firefox will soon be vulnerable to online attacks.') }}</p>
       </div>
 
       <div id="details-content">