UserAgent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:21.0) Gecko/20100101 Firefox/21.0

Steps to reproduce the problem:
press skift+alt+m to open the files app
1. the app close directly

2. 
3. 

What is the expected behavior?
the files app should remain open

What went wrong?
the app closes directly

Did this work before? Yes 2 or 3 canary version back

Chrome version: latest canary  Channel: canary
OS Version: 
Flash Version: