First, an 8x8 font must be loaded. To do this, /etc/rc.conf should contain the line (change the font name to an appropriate one for your locale):

font8x8="iso-8x8"		# font 8x8 from /usr/share/syscons/fonts/* (or NO).

The command to actually switch the mode is vidcontrol(1):

% vidcontrol VGA_80x60

Various screen-oriented programs, such as vi(1), must be able to determine the current screen dimensions. As this is achieved this through ioctl calls to the console driver (such as syscons(4)) they will correctly determine the new screen dimensions.

To make this more seamless, one can embed these commands in the startup scripts so it takes place when the system boots. To do this is add this line to /etc/rc.conf

allscreens_flags="VGA_80x60"	# Set this vidcontrol mode for all virtual screens
	  

References: rc.conf(5), vidcontrol(1).