Anyone having the missing file problem during compilation on slackware 10.0 & current should alter the Makefile and add the following string:
CFLAGS=... -I/usr/include/mozilla-1.7 ...
Its because certain header files are placed here. Maybe it's different on Fedora of SuSE.
Hope it helps someone,
Have a nice day.
This is probably due to a broken package config file included with mozilla. Use the gecko-sdk or hand edit the makefile to compile.