Steps to reproduce:

1. Go to a long article in Firefox.
2. Scroll to a section towards the end.
3. Open VisualEditor from the section-edit link.
4. Watch VisualEditor move the screen back to the top and place your cursor at the beginning.

This was reported in "latest Firefox" on Windows and reproduced with only slight variations in scroll in Firefox 39 on Mac 10.10. The behavior may be different (e.g., no scrolling at all) the first time you open it, and other times it scrolls down a couple of lines, but it never scrolls to the correct position.