Add mobile to JS, fix up python firefox link.

index.html

@@ -50,6 +50,9 @@
       <li next-group="ff-js">Firefox
         <div class="extra">did you know that all of the UI is written in JS?</div>
       </li>
+      <li target="https://wiki.mozilla.org/Mobile/Get_Involved">Mobile Firefox
+        <div class="extra">it's the Gecko engine, with an Android-specific UI. No Android device required.</div>
+      </li>
       <li target="http://github.com/mozilla/pdf.js">pdf.js
         <div class="extra">a PDF viewer written entirely in Javascript</div>
       </li>
@@ -89,7 +92,7 @@
     <span class="question">So you enjoy the paradigm of backtrace-driven development? That's cool, everyone gets a bit tired of
       static typing once in a while. You can work on</span>
     <ul class="choices">
-      <li target="http://developer.mozilla.org/En/Introductione">Firefox
+      <li target="http://developer.mozilla.org/En/Introduction">Firefox
         <div class="extra">lots of code is generated by python scripts</div>
       </li>
       <li target="https://blog.mozilla.com/webdev/get-involved/">Web development