I've not worked with a Mac for too many years to admit so I'll be of little help.
WinDoze uses a command, netstat, which shows all the computer's connections including ports. That will typically "find" the http daemon (Apache, IIS, etc) OR Skype using Port 80. Since it's first come, first served, that's what determines the application which "owns" the port.
It looks like your Dropbox "owns" the port (although it looks like it's port 53489, not port 80) but something (Dropbox) is listening to port 80 for connections.
I hope you can find something in all that which helps.