Steps to replicate the issue (include links if applicable):
- Similar to the issue with the contributions page, the preview of the wikitext 2017 editor also suffers from a layout issue.
- There is a big empty column on the left, caused by the insertion of the h1 firstHeading. in the dialog.
What should have happened instead?:
Not this ;)
Software version (skip for WMF-hosted wikis like Wikipedia):
Other information (browser name/version, screenshots, etc.):