Megamenu module does not open in Joomla backend (Firefox)

Today I have update my site to Joomla 3.6.3 and I had to change something in Mega Module.
When I go in W7 Firefox in the backend of Joomla to the module JUX Mega Menu I see for 1 sec flashing up the normal module settings and after that a white screen with only one dropdown 'Selct menu'. Browser is spinning to open more bot nothing is coming.
..../administrator/index.php?option=com_modules&view=module&layout=edit&id=231
So I can not use Firefox to do maintenance.

I also tried Chrome, this is working OK.

Hi Nico.
Thank you for using our product.
Please give me link your site and your account of the administrator via mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
I will check it for you

I am having the same problem with backend. I click to edit JUX module and see params for a second then goes to white screen with only selectbox in corner.

Please help, it is not possible for me to give you access.

J 3.6.4 & JUX 3.2.4

HI Bryan.
You can give me your link and your account of the administrator via my mail. I will check it for you