10.3.5 update kills all lizards and birds?

Howdy.  Yesterday I did a Software Update to get 10.3.5 installed on my 
PB 15" 1.5Ghz.  (Adding extra info if it helps).

I do a bit of web dev so I have quite a number of Mozillas and Fire***** 
lying around.  All of them, from Mozilla 1.6 to Firefox nightly, crash 
during startup.

Running from the command line I get:

socrates:/Applications/Firefox Nightly.app/Contents/MacOS paul$ ./firefox
./run-mozilla.sh: line 423:  1298 Bus error               "$prog" ${1+"$@"}

I moved my ~/Library/Application Support/Firefox out of the way, but it 
didn't help.

I tried non-mozilla.org builds (like Bjarne's SVG build) and got the 
same thing.  I'm now getting the source and trying a compile to see what 
happens.

Since there is no firestorm in the mozillazine forums or this newsgroup, 
I suspect there's some good reason that points the finger at my setup. 
Any suggestions on how I can collect info on what's happening?

--Paul