gmake -C gtk2 libs
nsDeviceContextSpecG.cpp
gmake[6]: Entering directory `/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/obj-x86_64-unknown-freebsd9.2/mozilla/widget/gtk2'
/usr/bin/clang++ -o nsDeviceContextSpecG.o -c -I../../dist/stl_wrappers -I../../dist/system_wrappers -include /tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/mozilla/config/gcc_hidden.h -DNATIVE_THEME_SUPPORT -DMOZ_GLUE_IN_PROGRAM -DXPCOM_TRANSLATE_NSGM_ENTRY_POINT=1 -DMOZILLA_INTERNAL_API -D_IMPL_NS_COM -DEXPORT_XPT_API -DEXPORT_XPTC_API -D_IMPL_NS_GFX -D_IMPL_NS_WIDGET -DIMPL_XREAPI -DIMPL_NS_NET -DIMPL_THEBES  -DSTATIC_EXPORTABLE_JS_API -DMOZ_THUNDERBIRD=1 -DNO_NSPR_10_SUPPORT -DOS_POSIX=1 -DOS_FREEBSD=1 -DOS_BSD=1  -DCAIRO_GFX -DMOZ_APP_NAME='"thunderbird"' -I/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/mozilla/ipc/chromium/src -I/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/mozilla/ipc/glue -I../../ipc/ipdl/_ipdlheaders  -I/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/mozilla/widget/gtk2 -I. -I../../dist/include  -I/usr/local/include/nspr -I/usr/local/include/nss -I/usr/local/include/nss/nss -I/usr/local/include -I/usr/local/include   -I/tmp/ports/
 usr/ports/mail/thunderbird/work/comm-esr24/mozilla/widget/gtk2/../xpwidgets -I/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/mozilla/widget/gtk2/../shared -I/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/mozilla/layout/generic -I/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/mozilla/layout/xul/base/src -I/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/mozilla/other-licenses/atk-1.0  -I/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/mozilla/widget/gtk2/../shared/x11  -fPIC -Qunused-arguments -isystem/usr/local/include  -Qunused-arguments -Wall -Wpointer-arith -Woverloaded-virtual -Werror=return-type -Wtype-limits -Wempty-body -Wsign-compare -Wno-invalid-offsetof -Wno-c++0x-extensions -Wno-extended-offsetof -Wno-unknown-warning-option -Wno-return-type-c-linkage -Wno-mismatched-tags -O2 -pipe -march=native -O3 -fno-strict-aliasing -fno-exceptions -fno-strict-aliasing -fno-rtti -ffunction-sections -fdata-sections -fno-exceptions -std=gnu++0x -pipe  -DNDE
 BUG -DTRIMMED -O2 -O3 -fomit-frame-pointer -!
 I/usr/local/include/cairo -I/usr/local/include/glib-2.0 -I/usr/local/include/pixman-1  -I/usr/local/include/freetype2 -I/usr/local/include/libdrm -I/usr/local/include/libpng15 -D_THREAD_SAFE -I/usr/local/include   -I/usr/local/include/cairo -I/usr/local/include/glib-2.0 -I/usr/local/include/pixman-1  -I/usr/local/include/freetype2 -I/usr/local/include/libdrm -I/usr/local/include/libpng15 -D_THREAD_SAFE -I/usr/local/include   -I/usr/local/include/pixman-1   -I/usr/local/include/startup-notification-1.0   -I/usr/local/include/gtk-3.0/unix-print -I/usr/local/include/gtk-3.0 -I/usr/local/include/at-spi2-atk/2.0 -I/usr/local/include/at-spi-2.0 -I/usr/local/include/dbus-1.0 -I/usr/local/include/dbus-1.0/include -I/usr/local/include/pango-1.0 -I/usr/local/include/harfbuzz -I/usr/local/include/gio-unix-2.0/ -I/usr/local/include/atk-1.0 -I/usr/local/include/cairo -I/usr/local/include/pixman-1  -I/usr/local/include/freetype2 -I/usr/local/include/libdrm -D_THREAD_SAFE -I/usr/local/include/gdk-
 pixbuf-2.0 -I/usr/local/include/libpng15 -pthread -I/usr/local/include/glib-2.0 -I/usr/local/include    -Qunused-arguments -isystem/usr/local/include  -DMOZILLA_CLIENT -include ../../mozilla-config.h -MD -MP -MF .deps/nsDeviceContextSpecG.o.pp  /tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/mozilla/widget/gtk2/nsDeviceContextSpecG.cpp
/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/mozilla/widget/gtk2/nsDeviceContextSpecG.cpp:578:5: error: no matching function for call to 'gtk_print_job_send'
    gtk_print_job_send(mPrintJob, print_callback, mSpoolFile, ns_release_macro);
    ^~~~~~~~~~~~~~~~~~
/usr/local/include/gtk-3.0/unix-print/gtk/gtkprintjob.h:96:26: note: candidate function not viable: no known conversion from 'void (GtkPrintJob *, gpointer, GError *)' to 'GtkPrintJobCompleteFunc'
      (aka 'void (*)(GtkPrintJob *, gpointer, const GError *)') for 2nd argument
void                     gtk_print_job_send                   (GtkPrintJob              *job,
                         ^
1 error generated.
gmake[6]: *** [nsDeviceContextSpecG.o] Error 1
gmake[6]: Leaving directory `/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/obj-x86_64-unknown-freebsd9.2/mozilla/widget/gtk2'
gmake[5]: *** [libs] Error 2
gmake[5]: Leaving directory `/tmp/ports/usr/ports/mail/thunderbird/work/comm-esr24/obj-x86_64-unknown-freebsd9.2/mozilla/widget'

Probably the directory structure is created incorrectly as there is directory for gtk2 and no directory for gtk3.