I can not attach any files using firefox in yahoo mail. My connection is working. I receive error 18. I tried everything in the forums but nothing worked.

Whenever I try to attach a photo or document (does not exceed size limit) I get this message. Please check your internet connection We are unable to communicate with your inbox. You can also reload the page to try to reconnect. Error 18 I have checked my connection and it is working. I am able to send and receive emails without attachments just fine. I cleaned out cookies and cache. I tried basic yahoo mail. I reconnected the internet...trying both wireless and ethernet. Nothing worked. Please advise. Thank you.