It's pf, not ipfw. You have to make your rule changes via the webGUI, otherwise they'll be overwritten. If your existing ruleset does not allow you into the webGUI, you can make temporary rule changes at the command line. Your running ruleset is /tmp/rules.debug. Info on changing it can be found here:
http://www.openbsd.org/faq/pf/
Don't do anything other than add a rule to permit access to the webGUI, then go into the webGUI and setup the same rule there, as well as whatever else you want. Editing the ruleset manually is unsupported and may cause problems, I strongly suggest having someone on the LAN side let you into the webGUI rather than doing this.
You could use tunneling with SSH to get into the webGUI, that's probably a better and easier solution.