mozilla-firefox-38.6.1esr-i686-1gv now depends of harfbuzz, but harfbuzz is not in repository, is in slack build.
When install
slapt-src -i harfbuzz
Show error
collect2: error: ld returned 1 exit status
make[3]: *** [test-unicode] Error 1
make[3]: se sale del directorio `/usr/src/slapt-src/libraries/harfbuzz/harfbuzz-0.9.19/test/api'
make[2]: *** [all-recursive] Error 1
make[2]: se sale del directorio `/usr/src/slapt-src/libraries/harfbuzz/harfbuzz-0.9.19/test'
make[1]: *** [all-recursive] Error 1
make[1]: se sale del directorio `/usr/src/slapt-src/libraries/harfbuzz/harfbuzz-0.9.19'
make: *** [all] Error 2
fakeroot -- sh harfbuzz.SlackBuild Error
so, I can't install firefox.

Regards