Firewall: Add command-line tool to rules (mosh-server) How can I add a command line tool I've installed manually to the system firewall? The tool is Mobile Shell (mosh) installed via the excellent Homebrew)?

Specifically, I want to add a rule for /usr/local/bin/mosh-server that allows incoming UDP traffic on 60001-60999.

I've tried using System Preference's Firewall pane and the "+" button, but I cannot seem to browse to /usr. I've configured Finder to display hidden and system files using TinkerTool, but that seemingly has no affect on the selection dialogue, which still hides /usr.

I've read a bit about using ipfw, but that's no longer available in Yosemite (v10.10). pfctl seems to be the replacement. I'll use these if I have to, but I'd much rather add an entry to the system firewall UI, so the change is discoverable.
I knew I was being dumb: in the Finder dialog that pops up, press Shift+⌘+G and enter /usr. From there I can browse to the binary.

Turns out this is a completely ordinary Finder shortcut for "Go to folder".