Yes. You can check the contents of a jail by running
$ firejail --list
to figure out the name of the jail (number at beginning of line) and now
$ firejail --fs.print=NAME
will list the contents, e.g.
$ firejail --fs.print=14840 | egrep "nsswitch|hosts"
Switching to pid 6150, the first child process inside the sandbox
clone /etc/hosts
clone /etc/hosts
Without nsswitch.conf the resolver will not even look at /etc/hosts as you can check by moving it away and running e.g.
$ strace nc localhost 99
resolv.conf is not that important since it usually points to localhost anyhow and nameservers can be overwritten per service with connmanctl or other dbus clients.
Probably, but that’s up to @martijntje, who spotted the problem.