www/firefox and poudriere: NotImplementedError: system provides too few semaphores

[O. Hartmann]

On a box running CURENT (FreeBSD 12.0-CURRENT #133 r316717: Tue Apr 11 22:53:06
CEST 2017 amd64), 16 GB RAM, 4-core XEON IvyBridge and jail:

Jail name:         head-amd64
Jail version:      12.0-CURRENT
Jail arch:         amd64
Jail method:       src=/usr/src
Jail updated:      2017-04-10 07:40:48

building/compiling www/firefox fails with the error shown below:

[...]
Creating config.status
Traceback (most recent call last):
  File "/wrkdirs/usr/ports/www/firefox/work/firefox-53.0/configure.py", line
124, in <module> sys.exit(main(sys.argv))
  File "/wrkdirs/usr/ports/www/firefox/work/firefox-53.0/configure.py", line
34, in main return config_status(config)
  File "/wrkdirs/usr/ports/www/firefox/work/firefox-53.0/configure.py", line
119, in config_status return config_status(args=[], **encode(sanitized_config,
encoding)) File
"/wrkdirs/usr/ports/www/firefox/work/firefox-53.0/python/mozbuild/mozbuild/config_status.py",
line 136, in config_status reader = BuildReader(env) File
"/wrkdirs/usr/ports/www/firefox/work/firefox-53.0/python/mozbuild/mozbuild/frontend/reader.py",
line 886, in __init__ self._gyp_worker_pool =
ProcessPoolExecutor(max_workers=max_workers) File
"/wrkdirs/usr/ports/www/firefox/work/firefox-53.0/python/futures/concurrent/futures/process.py",
line 274, in __init__ _check_system_limits() File
"/wrkdirs/usr/ports/www/firefox/work/firefox-53.0/python/futures/concurrent/futures/process.py",
line 263, in _check_system_limits raise NotImplementedError(_system_limited)
NotImplementedError: system provides too few semaphores (30 available, 256
necessary)
[...]

I run some other boxes in the lab, larger memeory (32 GB and 64GB), they do now
show this error. What causes it and how can I fix it?

Please CC me, I'm not a subscriber of the ports list.

Thanks in advance,

Oliver