User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0 Build ID: 20160919004008 Steps to reproduce: I entered "localhost:7654" into the address bar and pressed enter Actual results: Firefox leads me to www.localhost.com:7654. Firefox will even do that if I enter "http://localhost:7654" now. This is absolutely unacceptable for an existing valid hostname (especially the notable "localhost" which should really ALWAYS resolve) and an obvious security problem. Expected results: localhost" or any other resolved hostname NEVER gets randomly changed EVER, even if the server refuses connections.