**Steps to replicate the issue** (include links if applicable):
* Make sure that "Do not show page content below diffs" is disabled in your preferences on en.WP.
* Go to a typical Watchlist diff link like https://en.wikipedia.org/w/index.php?title=Wikipedia:Village_pump_(technical)&curid=3252662&diff=1203893569&oldid=1203863882&title=Wikipedia%253AVillage_pump_(technical)
**What happens?**:
* Observe that the full rendered page does not display below the diff.
* The text "&diffonly=1" is appended after the URL in the browser's address bar
**What should have happened instead?**:
* The full rendered page should display below the diff.
* The URL should not have the extra text appended.
**Software version** (skip for WMF-hosted wikis like Wikipedia):
**Other information** (browser name/version, screenshots, etc.):
This just started happening on en.WP less than one hour ago.