Merge pull request #722 from karansapolia/fix-for-591 r=@shane-tomlinson

fix(style): set line-height to improve global body legibility

Author: Shane Tomlinson

packages/fxa-content-server/app/styles/modules/_update_firefox.scss

@@ -0,0 +1,3 @@
+#fxa-update-firefox {
+    line-height: 24px;
+}

packages/fxa-content-server/server/templates/pages/src/update_firefox.html

@@ -26,7 +26,7 @@ <h1 id="fxa-update-firefox-header">{{#t}}Firefox update required{{/t}}</h1>
           </header>
 
           <section>
-            <p>
+            <p id="fxa-update-firefox">
               {{#t}}Firefox Accounts makes use of features that are not supported in your version of Firefox. Please download and install the latest version of Firefox to continue.{{/t}}
             </p>
             <div class="button-row">