To launch a desktop application from the host,
$ function lxc-launch() {
> sudo lxc-attach --clear-env -n $CONTAINER -- sudo -u ubuntu -i env DISPLAY=$DISPLAY $@
> }
$ CONTAINER=ubuntu-dev lxc-launch firefox
To launch an application from inside an lxc terminal session.
$ lxc-console -n $CONTAINER
# login to your user account
$ export DISPLAY=:0 # or whatever host $DISPLAY variable is set to.
$ inkscape
References: