Description:
Adding a check box or radio button in a form results in an replacement image instead of the box or the button. I have the same problem creating them from the list of controls or by adding a yes/no field. It seems that icons are missing. 
Nevertheless, I have functioning check boxes in my forms, and I can use copy-paste to create other check boxes.
I tried starting with a fresh profile, but it does not help.

Steps to Reproduce:
1.Opening a form in editing mode
2.Trying to add a radio button or a check box
3.

Actual Results:  
An image (representing a missing icon?) 

Expected Results:
a functional check box or radio button


Reproducible: Always

User Profile Reset: Yes, but it did not help

Additional Info:


User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:51.0) Gecko/20100101 Firefox/51.0