Is there an add-on that will block ad blockers?
I imagine it would be fairly easy to write - placing some code mimicking the ad code at the beginning of the script. If the code runs, the forums load in the user's browser. If the code is blocked, the user is send to a page that asked them to "allow" the site to run ads (I believe many ad blockers have such a feature). Alternately, the redirect page could simply say, "you have to turn off your ad blocker in order to view this site."