Hello, Firefox uses the Google Safe Browsing blacklist service to protect users from visiting sites that are harmful or deceptive (that is, they contain a fake banking website or something similar indended to steal user data). If Google detected your website as deceptive, it is possible that someone had hacked into it and added those fake sites. Please check your website for any deceptive pages, and after you make sure it's clean and hacker-proof, you can request to remove your site from Google's blacklist (you can find the link on the "Deceptive site ahead" page). Regards, Lan