Hi,

I didn't see any resolution to your post. my experience may assist in 
solving it.

upgrading my 4Beta2 system from January daily to a daily from Oct 31 
solved my problem. I was quite careful in tracking each change I made to 
the system. Nothing worked until that change.

NetBSD magnet.clubs 4.0_RC3 NetBSD 4.0_RC3 (XEN3_DOM0) #0: Wed Oct 31 
16:16:01 PDT 2007 
builds@wb34:/home/builds/ab/netbsd-4/i386/200710310002Z-obj/home/builds/ab/netbsd-4/src/sys/arch/i386/compile/XEN3_DOM0 
i386

I have used almost every 2.0.0.x release on NetBSD and they made no 
change. About 2.0.0.7 firefox I resolved to look into it further. I 
upgraded to 2.0.0.8 and it made no difference. I then upgraded my kernel 
and userland to a more recent daily and the problem went away. Im using 
the system packages for X11 not modular.

switching images off or increasing the limits only made marginal 
improvements. disabling all plugins/add-ons or running in safe mode made 
no change.

I have to think that even if the fault was/is in firefox, the failures 
were caused by an interaction with x11 or userland libraries and no 
other pkgsrc package.

Simon