Steps to reproduce:
- go to any page at http://en.wikipedia.beta.wmflabs.org/
- edit the page with visual editor
- popup appears with text: Error loading data from server: internal_api_error_ErrorPageError: Exception Caught: The content format json is not supported by the content model wikitext.. Would you like to retry?
Version: unspecified
Severity: normal
OS: Mac OS X 10.8
Platform: Macintosh