I am not able to register, or now sign in to Kongregate on Mozilla Firefox. When I registered (tried to, anyway) it said “captcha validation CAPTCHA not found”. I think that is still the problem. I had to use Internet Explorer.
I myself have quite a few we browsers at my disposal to use but i mostly use FF or IE cause they are the easiest available for me to use. I use FF the most and make sure i have everything up-to-date for it so i dont have to worry about any of this but for now update it and periodically make sure you have all the right things for it