/usr/share/examples/ipfw/change_rules.sh uses not supported base system diff switch -F, which is probably supported by the GNU diff, but not the base system one. So basically the script is broken now.

Shame on one who has commited it.

===Cut===
[...]
:wq
/etc/rc.firewall.ronin.new: 316 строк, 12341 символов
Do you want to install the new rules (Y/N) ? Y
The rules will be changed now. If the message 'Type y to keep the new
rules' does not appear on the screen or the y key is not pressed in 30
seconds, the original rules will be restored.
The TCP/IP connections might be broken during the change. If so, restore
the ssh/telnet connection being used.
Would you like to see the resulting new rules (Y/N) ? n
Type y to keep the new rules (Y/N) ? Y
The new rules are now installed. The previous rules have been preserved in
the file /etc/rc.firewall.ronin.201907301121
diff: invalid option -- F
usage: diff [-aBbdilpTtw] [-c | -e | -f | -n | -q | -u] [--ignore-case]
            [--no-ignore-case] [--normal] [--strip-trailing-cr] [--tabsize]
            [-I pattern] [-L label] file1 file2
       diff [-aBbdilpTtw] [-I pattern] [-L label] [--ignore-case]
            [--no-ignore-case] [--normal] [--strip-trailing-cr] [--tabsize]
            -C number file1 file2
       diff [-aBbdiltw] [-I pattern] [--ignore-case] [--no-ignore-case]
            [--normal] [--strip-trailing-cr] [--tabsize] -D string file1 file2
       diff [-aBbdilpTtw] [-I pattern] [-L label] [--ignore-case]
            [--no-ignore-case] [--normal] [--tabsize] [--strip-trailing-cr]
            -U number file1 file2
       diff [-aBbdilNPprsTtw] [-c | -e | -f | -n | -q | -u] [--ignore-case]
            [--no-ignore-case] [--normal] [--tabsize] [-I pattern] [-L label]
            [-S name] [-X file] [-x pattern] dir1 dir2
Null message body; hope that's ok
===Cut===