Advice on Build Procedure

[Dave]

Folks,
I've recently downloaded and built the mozilla firefox code, and
produced a running distribution. I've a few questions about the build
process which I can't seem to find the anwsers to on the website.

I'm used to using a build system where there is a 'Makefile' in every
sub directory, so if I just want to build the code in a sub directory
I run 'make all'

The only instructions I've found for building mozilla require me to go
to the topsrcdir and run 'make -f client.mk build'

If I edit one cpp file in a sub directory is there an easy way for me
to rebuild it ?

Thanks