Dave, everyone...
Hi Dariusz, since everyone else is running it fine and it only fails for you when Firefox is open and you're using LIBPATHSTRICT, it seems the most likely is resource starvation, and memory makes sense.
...
Yup!
Messing around with VIRTUALADDRESSLIMIT (by making it larger) gets me a working Kompozer install here. Granted, this is only a half-win at best because whatever amount I increase that setting by is certainly taking away from the fs cache, and I'm sure not going to give up my giant JFS cache...LOL!
Anyways...I have my answer though.
So I'm curious: is no one else running this with LIBPATHSTRICT setting like I am?

Heck, maybe the simplest solution yet - which I haven't actually tried given that the DLLs between Kompozer and our current FF would be so different - would be to drop all the provided DLLs and try to use the FF ones?
OK..another test, here we go...
