This addon is to simulate different vision conditions. If for example you have deuteranopia then selecting the deuteranopia filter won't do anything for you as it will change the website to look colour-wise like it would look to someone with deuteranopia.
I am not quite sure what you were expecting when using the deuteranopia filter to simulate deuteranopia?
Just to ensure that the addon works correctly have you tried one of the pther filters, like inverted colours or blur?
Also make sure you're not testing on the Firefox addons website as the domain has a built-in block for addons to change anything.