chore: further unify Puppeteer-Firefox tests with Puppeteer (#3931)

This patch:
* unifies assets between tests
* enables a few puppeteer tests on Puppeteer-Firefox

Drive-by: beautify failing output of `expect.toEqual` matcher.

References #3889

test/assets/wrappedlink.html

@@ -26,4 +26,7 @@ a {
   <a href='#clicked'>123321</a>
 </div>
 <script>
+  document.querySelector('a').addEventListener('click', () => {
+    window.__clicked = true;
+  });
 </script>