Steps to reproduce (experienced in Chromium 54.0.2840.71):
- Open a page with a table in VisualEditor (for example https://en.wikipedia.org/wiki/Pushing_Daisies?veaction=edit )
- Click on a column header, then on the column menu
- Click "Insert before" or "Insert after".
Expected result: A column is inserted.
I thought this may be related to the Chrome support issue that @Jdforrester-WMF mentioned to me recently, but I noticed that there was also an issue in Firefox (50.0.2), although with a different error in the console: "TypeError: dataMatrixLine is undefined". I'm opening this report so that someone more knowledgeable than me can determine if this is a known issue.