Permission denied to access property 'type' in Firefox with jQuery

Permission denied to access property 'type' in Firefox with jQuery

Hi everyone,

I have been logging the most frequent Javascript errors on Freeciv-web  using Track:js and 
have discovered  that the most frequently occuring error on Freeciv-web is the following Javascript error:

File: https://play.freeciv.org/javascript/jquery.min.js : 3 | 2856
Error: Permission denied to access property 'type'

The error only occurs on Firefox, not any other browser. The error occurs initially on the first page load when starting a new game (url is /webclient ).

Stack Trace/ Error Origination:
n.event.add/r.handle@ https://play.freeciv.org/javascript/jquery.min.js :3:2857

jQuery version 2.1.2-pre 4e7f34f6296111f7f91d621397dfb02c6bf4c41f  
jQuery UI version  1.11.2

Any help resolving this issue would be greatly appreciated!

Andreas