Steps to replicate the issue (include links if applicable):
- Open Special:AbuseFilter/history/1/diff/prev/27863
- change diff mode from wikitext to visual
What happens?: server returns error
What should have happened instead?: In the first place, it should not be possible to change
Software version (skip for WMF-hosted wikis like Wikipedia): WMF-hosted
Other information (browser name/version, screenshots, etc.):