In order to have Firefox launch a gnome-terminal for url which begin in ssh/telnet, I wrote a little script and made some changes in about:config
prefs.js
user_pref("network.protocol-handler.app.telnet", "/home/asyd/bin/firefox-handler.zsh"); user_pref("network.protocol-handler.app.ssh", "/home/asyd/bin/firefox-handler.zsh");
firefox-handler.zsh
#!/bin/zsh url=$1 proto=${url//:*/} data=${${url//*:\/\//}%/} /usr/bin/gnome-terminal -e "$proto $data"