To get the spice xpi working use the following steps:
1. Install the spice-client package which gives you /usr/bin/spicec
2. Extract the libnsISpicec.so file from the latest Fedora (FC19) spice-xpi RPM.
3. Placed it in /usr/lib/mozilla/plugins/
4. Restart Firefox.
After restarting Firefox, you can now view the console from RHEV/OVIRT.
On Debian you can use the sid repo and install browser-plugin-spice