I kind had some problem with firefox 3.0.3 recently, it just hanging on loading pages and nothing responsed (not crash), and you can't close any tab eihter. Fist I though it's my network connection problem but Safari works fine at the same time the same web sites. Then I start wondering if it is a firefox problem which I'm using Neil's build, and the official firefox looks fine (but later I met the same issue with offical firefox), so, it's pretty much why I start build my own version firefox follow by MDC.

after building and testing, I found 3.0.4pre, 3.0.3, 3.0.2 all have the same issue, ran out of idea.

Why not just offical firefox?
Well, it's just a little bit too slow in javascript performance.

Here is my .mozconfig

. $topsrcdir/browser/config/mozconfig

#mk_add_options AUTOCONF=autoconf213
#export CC=gcc-4.0
#export CXX=g++-4.0

export MOZ_OPTIMIZE_LDFLAGS="-opt:ref,icf"
mk_add_options MOZ_OPTIMIZE_LDFLAGS="-opt:ref,icf"

mk_add_options MOZ_OBJDIR=@TOPSRCDIR@/obj-@CONFIG_GUESS@
mk_add_options PROFILE_GEN_SCRIPT='$(PYTHON) $(MOZ_OBJDIR)/_profile/pgo/profileserver.py'
#mk_add_options MOZ_MAKE_FLAGS="-s -j4"
mk_add_options MOZ_MAKE_FLAGS="-j8"
mk_add_options MOZ_CO_PROJECT=browser

## intel
ac_add_options --enable-optimize='-O3 -march=prescott -pipe -mfpmath=sse,387 -fforce-addr -mieee-fp -msse3 -msse2 -msse -mmmx -ftree-loop-linear -fivopts -malign-natural -fsched-interblock -fstrict-aliasing'

## testing/profiling
ac_add_options --disable-debug
ac_add_options --disable-tests
ac_add_options --disable-mochitest 
ac_add_options --disable-pedantic

## platform
ac_add_options --disable-activex
ac_add_options --disable-activex-scripting
ac_add_options --enable-macos-target=10.4
ac_add_options --with-macos-sdk=/Developer/SDKs/MacOSX10.5.sdk
# ppc
#ac_add_options --enable-prebinding


## commonly used
ac_add_options --with-distribution-id=com.creativecrap.minefield
ac_add_options --enable-official-branding 
#ac_add_options --with-branding=/path/to/branding

ac_add_options --enable-application=browser
ac_add_options --enable-libxul --disable-static
#ac_add_options --enable-static --disable-libxul
ac_add_options --disable-crashreporter
#ac_add_options --disable-javaxpcom

## other options
ac_add_options --disable-accessibility
ac_add_options --enable-profile-guided-optimization 
ac_add_options --enable-strip
ac_add_options --enable-reorder
ac_add_options --enable-crypto
ac_add_options --enable-single-profile
ac_add_options --enable-pthreads
ac_add_options --enable-svg
ac_add_options --enable-canvas
ac_add_options --enable-accessibility
ac_add_options --enable-cairo
ac_add_options --enable-default-toolkit=cairo
ac_add_options --enable-default-toolkit=cairo-cocoa
ac_add_options --disable-shared
ac_add_options --disable-updater
ac_add_options --disable-composer
ac_add_options --disable-ldap
ac_add_options --disable-mailnews
ac_add_options --disable-profilesharing
#ac_add_options --enable-extensions=default
#ac_add_options --disable-jsd
#ac_add_options --enable-static-libs
#ac_add_options --disable-installer

ac_add_options --without-system-nspr
ac_add_options --without-system-zlib
ac_add_options --without-system-png
ac_add_options --without-system-jpeg
ac_add_options --without-system-mng

sure build with PGO:
make -w -f client.mk clean profiledbuild

make dmg package, in the @obj-dir/dist/
make package

This is not the fastest optimized configure I had build, but the last one, and the test result from Sun Spider is 8430.6ms. The fastest build is 4207.8ms with -ffast-math but it's a lot of javascript will fail to run, and the rest of build are all around 8235ms ~ 8460ms.