When button is disabled, it’s not-clickable in all browsers. However in Firefox and Chrome, the button looks enabled, though the user cannot click it.

Reason:

From W3Scholl, "Enabled" Property isn't standard property of XHTML 4.

Solution:

You can modify the way they look with CSS

button[disabled] { 
 color:Grey;
/* Add other  styles here for disable button */ 
}