Well, I found where the cookies are:

/home/user/.mozilla/microb/cookies.txt

But when I open that file, it starts with:

# HTTP Cookie File
# http://wp.netscape.com/newsref/std/cookie_spec.html
# This is a generated file! Do not edit.
# To delete cookies, use the Cookie Manager

After that message, there is a list of cookies.

My feeling is that the message is a leftover from the code on which MicroB is based.

If not, where is said "Cookie Manager"?

I suppose from that message that editing that file would be pointless or harmful, but I'm tempted to do it. Any thoughts?