===>  firefox-esr-24.1.0_1,1 conflicts with installed package(s):
      firefox-25.0_1,1

      They install files into the same place.
      You may want to stop build with Ctrl + C.
===>   firefox-esr-24.1.0_1,1 depends on file: /usr/local/sbin/pkg - found
===> Fetching all distfiles required by firefox-esr-24.1.0_1,1 for building

===>  firefox-esr-24.1.0_1,1 conflicts with installed package(s):
      firefox-25.0_1,1

      They will not build together.
      Please remove them first with pkg delete.
*** Error code 1

Stop.
make: stopped in /usr/ports/www/firefox-esr