Puzzling error messages from 'make'

[walt <wa1ter@xxxxxxxxxxxxx>]

I've been trying for two days to build firefox from pkgsrc,
but the build always halts with this error which I can't
decipher:

ranlib libjsurl_s.a
/usr/pkgsrc/www/firefox/work/mozilla/config/nsinstall -R -m 644 libjsurl_s.a
. ./../../dist/lib
make[4]: Leaving directory `/usr/pkgsrc/www/firefox/work/mozilla/dom/src/jsurl'
make[4]: write error
make[3]: *** [libs] Error 1
make[3]: Leaving directory `/usr/pkgsrc/www/firefox/work/mozilla/dom/src'
make[2]: *** [libs] Error 2
make[2]: Leaving directory `/usr/pkgsrc/www/firefox/work/mozilla/dom'
make[1]: *** [tier_9] Error 2
make[1]: Leaving directory `/usr/pkgsrc/www/firefox/work/mozilla'
gmake: *** [default] Error 2
*** Error code 2

Note that the 'write error' comes from 'make', not from 'gmake'.

I have tons of space left on the disk, and the error always occurs at
the same spot in the build -- I don't think this is a hardware problem.
I'm doing the build as root, so fileperms shouldn't be the problem.

First, can anyone reproduce this error?

Can anyone translate this line into English for me:
make[3]: *** [libs] Error 1

Who is printing the *** and what does it mean?  What does the [libs]
refer to?  Who is printing the 'Error 1' and what does it mean?

Why does the final error message come from 'gmake' instead of 'make'?
IIRC the order is more often the other way around (but I'm guessing).

Thanks for any hints!