Error getting my website on some browsers

Well i have this website made with wordpress hosted on hostgator in a web hosting. Sometimes when i access it with some browsers like firefox it give my this error:

The text is in spanish but it basicly says:

"The conection is not safe The owner of www.domain.com has configured this website incorrectly. To protect your information againts thefts, Firefox has not connected to this site"

Sorry for my english.

Thanks!