Wrong XML analysis: Undefined entity

Hi, I am using Czech N360 version 20.3.1.22 with NT 2013.3.5.1 installed on FireFox 21.0 and I have a problem since FF 17.0 (and previous versions of N360 and NT) with annoying Norton Toolbar. It displays Wrong XML analysis: Undefined entity message on every webpage that includes input fields, see bellow (I have translated an error messages into English):

NT-NIS.jpg

 

I have reinstalled my PC a few days ago and I thought it would solve this problem. Unfortunatelly, it is still the same. Anyway, all passwords work correctly on any website I use.

 

Edit:
It should looks like this in IE:

NT-NIS in IE.jpg