# cd /usr/src/mozilla/
# ./configure
loading cache ./config.cache
checking host system type... i386-unknown-freebsd4.7
checking target system type... i386-unknown-freebsd4.7
checking build system type... i386-unknown-freebsd4.7
checking for gcc... gcc
checking whether the C compiler (gcc  ) works... yes
checking whether the C compiler (gcc  ) is a cross-compiler... no
checking whether we are using GNU C... yes
checking whether gcc accepts -g... yes
checking for c++... c++
checking whether the C++ compiler (c++  ) works... yes
checking whether the C++ compiler (c++  ) is a cross-compiler... no
checking whether we are using GNU C++... yes
checking whether c++ accepts -g... yes
checking for ranlib... ranlib
checking for as... /usr/bin/as
checking for ar... ar
checking for ld... ld
checking for strip... strip
checking for windres... no
checking for gawk... no
checking for mawk... no
checking for nawk... nawk
checking whether gcc and cc understand -c and -o together... yes
checking how to run the C preprocessor... gcc -E
checking how to run the C++ preprocessor... c++ -E
checking for a BSD compatible install... /usr/bin/install -c
checking whether ln -s works... yes
checking for perl5... /usr/bin/perl5
checking for minimum required perl version >= 5.004... 5.00503
checking for full perl installation... yes
checking for doxygen... :
checking for whoami... /usr/bin/whoami
checking for autoconf... :
checking for unzip... /usr/local/bin/unzip
checking for zip... /usr/local/bin/zip
checking for makedepend... /usr/X11R6/bin/makedepend
checking for xargs... /usr/bin/xargs
checking for gmake... no
checking for make... /usr/bin/make

*** /usr/bin/make is not GNU Make.  You will not be able to build Mozilla without GNU Make.