It happens to me multiple times today: I was unable to save a changed page due to a JS error: "Cannot open another window while another one is active" using Firefox 26 beta.

Steps to reproduce:

1. Open https://sv.wikipedia.org/wiki/Miikka_Anttila in VE mode
2. Go to bottom of the page
3. Add the template "Commonscat" without parameters
4. Try to save

Version: unspecified
Severity: normal
URL: https://sv.wikipedia.org/wiki/Miikka_Anttila