Hi

Firefox is a web browser. For you to do what you are looking to achieve, you will need to sign up for an on-line fax service that will allow you to send electronic documents to a fax number and to receive electronic images in your browser of faxes that you have been sent.

I recommend you search for such a service on-line, but this is not a service that Mozilla currently provides.

If you are using an All-in-One printer that has Fax capabilities, look at your Printer Software for the PC-Fax feature, or whatever your brand of Printer calls it.

I have a Brother All-in-One Inkjet printer and I access the Scan, PC-Fax, and other features thru the CommandCenter3 software icon in the Windows 7 System Tray, Your Printer should have a similar icon, or look in Start > Programs -> your Printer name.