Firefox doesn't have any built-in prompts about allowing cookies, so the page is generating the query and, for some reason, failing to keep track of your response. Normally sites use a cookie to keep track of your cookie preferences, so perhaps its ability to save cookies is blocked by a Firefox setting? If you look at the left end of the address bar, you should see a shield icon and a lock icon. Sometimes there is a third icon with two lines that shows customized permissions for the site. If you click the shield icon to drop the Tracking Protection panel, it may indicate whether cookies are being blocked for the main site or any site from which images, scripts or other embedded content are being retrieved into the page. Can you see any cookies being blocked there from a source that looks like you might need to make an exception?