These experimental palemoon packages have been built on Solaris 11.4

$ beadm list
BE Name Flags Mountpoint Space Policy Created          
------- ----- ---------- ----- ------ ---------------- 
solaris NR    /          6.97G static 2021-01-22 20:23 

$ cat /etc/release 
                             Oracle Solaris 11.4 X86
  Copyright (c) 1983, 2018, Oracle and/or its affiliates.  All rights reserved.
                            Assembled 16 August 2018

$ gcc --version
gcc (GCC) 7.3.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ cat .mozconfig
# Clear this if not a 64bit build
_BUILD_64=1

# 8 vCPU
mk_add_options MOZ_MAKE_FLAGS="-j6"

# Clear this to build for Solaris
#_BUILD_ILLUMOS=1

# Standard build options for Pale Moon
ac_add_options --enable-application=palemoon
ac_add_options --enable-optimize="-O2 -w"
ac_add_options --enable-default-toolkit=cairo-gtk3
ac_add_options --enable-jemalloc
ac_add_options --enable-strip
ac_add_options --enable-devtools
ac_add_options --enable-av1
# DISABLED needs gcc-10 # ac_add_options --enable-jxl
ac_add_options --disable-webrtc
ac_add_options --disable-gamepad
ac_add_options --disable-tests
ac_add_options --disable-debug
ac_add_options --disable-necko-wifi
ac_add_options --disable-updater
ac_add_options --with-pthreads

# SunOS requires this because the GNU toolchain is not the default
ac_add_options --with-toolchain-prefix=g

# Please see https://www.palemoon.org/redist.shtml for restrictions when using the official branding.
ac_add_options --enable-official-branding
export MOZILLA_OFFICIAL=1
export CONFIG_SHELL=/usr/bin/bash

if [ -n "$_BUILD_ILLUMOS" ]; then
  export MOZ_PKG_SPECIAL=illumos
fi

if [ -n "$_BUILD_64" ]; then
  ac_add_options --libdir=/usr/lib/amd64
  ac_add_options --x-libraries=/usr/lib/amd64
  export PKG_CONFIG_PATH=/usr/lib/amd64/pkgconfig
else
  ac_add_options --target=i386-pc-solaris2.11
  ac_add_options --host=i386-pc-solaris2.11
  ac_add_options --libdir=/usr/lib
  ac_add_options --x-libraries=/usr/lib
  export PKG_CONFIG_PATH=/usr/lib/pkgconfig
fi