This tests for regression against REGRESSION: parse mode gets set to strict after going back from non-HTML content

  1. Click on PDF link below. Wait for PDF to fully load.
  2. Click "Back" button once.
  3. Click the link again.
  4. Click "Back" button once.

In the failing case, the thin line above the link will get much thicker. If it remains the same, this test has passed.