untrusted comment: verify with openbsd-66-base.pub
RWSvK/c+cFe24MoLrjsz70R9znTIfudTm17CZajtkSiAAfulx5XX5OS6lTvEFcuecEJRuMlywWUMMziVj2oPcwFkOhQNLdli/Qo=

OpenBSD 6.6 errata 005, November 16, 2019:

A new kernel may require newer firmware images. Make sysupgrade
opportunistically update firmware images.

Apply by doing:
    signify -Vep /etc/signify/openbsd-66-base.pub -x 005_sysupgrade.patch.sig \
        -m - | (cd /usr/src && patch -p0)

And then rebuild and install sysupgrade:
    cd /usr/src/usr.sbin/sysupgrade
    make obj
    make
    make install

Index: usr.sbin/sysupgrade/sysupgrade.sh
===================================================================
RCS file: /cvs/src/usr.sbin/sysupgrade/sysupgrade.sh,v
retrieving revision 1.25
diff -u -p -r1.25 sysupgrade.sh
--- usr.sbin/sysupgrade/sysupgrade.sh	28 Sep 2019 17:30:07 -0000	1.25
+++ usr.sbin/sysupgrade/sysupgrade.sh	12 Nov 2019 21:18:29 -0000
@@ -197,6 +197,9 @@ rm -f /home/_sysupgrade/{${CLEAN}}
 __EOT
 fi
 
+echo Fetching updated firmware.
+fw_update || echo "Warning: firmware not updated."
+
 install -F -m 700 bsd.rd /bsd.upgrade
 sync