Any possibility of making a pay-to-use Firefox extension?
earl: Does the license even permit this?  I'm not going to do the legwork for you, but I'd examine this very carefully with the help of a lawyer who has worked on these sorts of issues before.  This may mirror the driver issue in the linux kernel -- even plugins may be contaminated by open source licenses.  (Contaminated used in the nicest way possible; I'm a big fan of OS licensing and software.)