Compiling firefox on Raspberry Pi 2

[bob prohaska]

Attempts to compile firefox63 on an RPI2 fail with
===>  rust-1.29.2 is only for aarch64 amd64 i386, while you are running armv6
(reason: requires prebuilt bootstrap compiler).
*** Error code 1

while compilation of firefox-esr stops with
dt_modtext:/usr/src/cddl/contrib/opensolaris/lib/libdtrace/common/dt_link.c(856): arm not implemented
dtrace: failed to link script /usr/ports/www/firefox-esr/work/firefox-52.8.0esr/js/src/devtools/javascript-trace.d: an error was encountered while processing jsarray.o
gmake[5]: *** [/usr/ports/www/firefox-esr/work/firefox-52.8.0esr/config/rules.mk:788: js-dtrace.o] Error 1
gmake[5]: Leaving directory '/usr/ports/www/firefox-esr/work/.build/js/src'
gmake[4]: *** [/usr/ports/www/firefox-esr/work/firefox-52.8.0esr/config/recurse.mk:71: js/src/target] Error 2
gmake[4]: Leaving directory '/usr/ports/www/firefox-esr/work/.build'
gmake[3]: *** [/usr/ports/www/firefox-esr/work/firefox-52.8.0esr/config/recurse.mk:33: compile] Error 2
gmake[3]: Leaving directory '/usr/ports/www/firefox-esr/work/.build'
gmake[2]: *** [/usr/ports/www/firefox-esr/work/firefox-52.8.0esr/config/rules.mk:523: all] Error 2

Can anybody suggest workaround for either problem?

Thanks for reading,

bob prohaska