fix(strings): modify success message (#5030) r=vladikoff

Fixes: #5012

app/scripts/templates/connect_another_device.mustache

@@ -1,7 +1,7 @@
 <div id="main-content" class="card">
   <header class="hidden" id="fxa-connect-another-device-header"><h1>{{#t}}Connect another device{{/t}}</h1></header>
   {{#isSignedIn}}
-    <div class="success success-authenticated visible">{{#t}}This device is connected{{/t}}</div>
+    <div class="success success-authenticated visible">{{#t}}This Firefox is connected{{/t}}</div>
   {{/isSignedIn}}
   {{^isSignedIn}}
     <div class="success success-not-authenticated visible">{{#t}}Email verified{{/t}}</div>