when user reaches container tab count, show achievement panel

webextension/popup.html

@@ -67,6 +67,34 @@
     <a href="#" id="onboarding-longpress-button" class="onboarding-button">Done</a>
   </div>
 
+  <div class="panel achievement-panel hide" id="achievement-panel">
+    <img class="onboarding-img" alt="You achieved a Containers milestone!" src="/img/onboarding-3.png" />
+    <h3 class="onboarding-title">100 tabs!</h3>
+    <p>You've opened 100 Container tabs.</p>
+    <p>If you enjoy Containers, help us spread the word!</p>
+    <p class="share-ctas">
+      <a class="cta-link" href="https://mzl.la/2gJtIZ4" id="achievement-rate-button" target="_blank">
+        <span class="cta amo-rate-cta">
+          <img src="/img/amo-icon.svg" class="cta-icon" alt="addons.mozilla.org Icon">
+          Rate
+        </span>
+      </a>
+      <a class="cta-link" href="https://bit.ly/fb-share-mac-addon" target="_blank">
+        <span class="cta fb-share-cta">
+          <img src="/img/webicon-facebook.svg" class="cta-icon" alt="Facebook Icon">
+          Share
+        </span>
+      </a>
+      <a class="cta-link" href="http://bit.ly/tweet-100-tabs-mac-addon" target="_blank">
+        <span class="cta tweet-cta">
+          <img src="/img/webicon-twitter.svg" class="cta-icon" alt="Twitter Icon">
+          Tweet
+        </span>
+      </a>
+    </p>
+    <a href="#" id="achievement-done-button" class="onboarding-button">Done</a>
+  </div>
+
   <div class="panel container-panel hide" id="container-panel">
     <div id="current-tab">
       <h3>Current Tab</h3>