[devtools] Use Xvfb to run firefox in js tests on posix platforms
This way we don't require running tests under X.
#! /bin/sh -e#if [ "$1" = configure ]; then if which install-docs >/dev/null 2>&1; then install-docs -i /usr/share/doc-base/cubicweb-doc fifi#DEBHELPER#exit 0