Thanks roytam1, I've just made it false, and restarted K-M, but no joy.
FWIW, Pale Moon 27.9.4 does not have dom.messageChannel.enabled in its config.
Just as odd, many other sites do show their reCapcha in K-M, and they work.
EDIT: Duh. D'oh! I forgot to unset my IE useragent string As soon as I put the default K-M UA, reCaptcha shows!
Forum:
K-Meleon on Goanna