General source code refactoring

tests/fixtures/extension.html

@@ -0,0 +1,13 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1">
+    <title>Extension Synthetic Integration Fixture</title>
+  </head>
+  <body>
+    <button id="open" type="button">Open Opportunities</button>
+    <script src="/fixture-runtime.js"></script>
+    <script src="/extension.js"></script>
+  </body>
+</html>