Steps to reproduce:
- Open VisualEditor on a long wiki page (https://en.wikipedia.org/wiki/Elephant?action=edit)
- Press PageDown
- The editing window moves to the end of the page, as if End was pressed.
- The editing window scrolls down one screen.
This occurs at any point the cursor is inserted, in visual or text editing mode, in Firefox or Chrome. PageUp always acts as Home and PageDown as End. In Article View mode (or any other usage on the same computer), PageUp and PageDown act as expected.