preinst is in firefox-locale-ja 11.0+build1-0ubuntu4.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | #!/bin/sh
set -e
MOZ_APP_NAME=firefox
MOZ_LIBDIR=/usr/lib/firefox
if [ "$1" = "install" ] || [ "$1" = "upgrade" ] ; then
# ${LIBDIR}/distribution was a symlink in 11.10
    if [ -h ${MOZ_LIBDIR}/distribution ] ; then
        rm -f ${MOZ_LIBDIR}/distribution
    fi
# This used to be a symlink
    if [ -h ${MOZ_LIBDIR}/distribution/searchplugins ]; then
        rm -f ${MOZ_LIBDIR}/distribution/searchplugins
    fi
fi
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