Hi, that seems to be a rather old Trojan from 2012 that hit over 600, 000 macs. There was also a Apple Update that from 2012 that should have caught that before Clam A/V. Did you download this from a site other than from a Official Mozilla site. If so should report the site as it may have been hacked and that payload was added to the download. You may want to give your self a scan with a Malware Scanner : https://www.malwarebytes.com/mac/ You can always get the current version Full Installer for a Mac here : *https://www.mozilla.org/firefox/all/ Please let us know if this solved your issue or if need further assistance.