Ужится в каком контексте ?
Если просто поставить и запустить оба сервера одновременно, то оно работает.
Если вопрос в том что бы они одновременно работали с более-менее серьезной загрузкой, вот это к сожалению не проверял.

FireBird RELNOTES:
There may be times, however, when you still get "semget failed"
even though the lock manager is not running and the semaphores have
been cleaned up. There seems to be a conflict with this release
and the PostgreSQL 7 release as installed from the ports collection.
If you're having trouble with Firebird and you're running PostgreSQL,
try stopping PostgreSQL:

/usr/local/etc/rc.d/pgsql.sh stop

and see if that helps. Alternatively, increase the value of SEMMNS
by 48 in your kernel configuration file. This can be found by getting
the current value with 'sysctl -a | grep semmns'. You can either add
this to your kernel config, or add the following line to /boot/loader.conf:

kern.ipc.semmns=X

where is is the current value plus 48. If this doesn't resolve the issue,
try adding 48 again.

From PostgreSQL 7.4 Docs:
FreeBSD
NetBSD
OpenBSD

The options SYSVSHM and SYSVSEM need to be enabled when the kernel is compiled. (They are by default.) The maximum size of shared memory is determined by the option SHMMAXPGS (in pages). The following shows an example of how to set the various parameters:

options SYSVSHM
options SHMMAXPGS=4096
options SHMSEG=256

options SYSVSEM
options SEMMNI=256
options SEMMNS=512
options SEMMNU=256
options SEMMAP=256

(On NetBSD and OpenBSD the key word is actually option singular.)

You might also want to configure your kernel to lock shared memory into RAM and prevent it from being paged out to swap. Use the sysctl setting kern.ipc.shm_use_phys.

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