Arrow keys triggers Lightbox in edit mode which makes navigating in the source text edit very hard.

Steps to reproduce:

1. Be logged in at https://www.mediawiki.org
2. Go to https://www.mediawiki.org/w/index.php?title=Language_portal&action=edit
3. Click "Preview" (second button below edit screen)
4. Place cursor in the edit area.
5. Click arraow "back" or "forward"

Observed:
I. Lightbox appears with MultimediaViewer

Expected:
II. Edit without interruptions.

Additional information:

• OSX 10.9 / Firefox 25.0.1
• MediaWiki 1.23wmf6 (rMWcc018cb82be3)
• MultimediaViewer (Versie 0.2.0)

Version: master
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=58873