alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET INFO Possible Firefox Plugin install"; flow:to_server,established; http.uri; content:".xpi"; nocase; fast_pattern; endswith; http.user_agent; content:"|20|Firefox/"; reference:url,research.zscaler.com/2012/09/how-to-install-silently-malicious.html; classtype:bad-unknown; sid:2016846; rev:6; metadata:created_at 2013_05_14, confidence Medium, signature_severity Informational, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_09_18;)