> tolerable cross platform toolkit

..for the 90s. There was very little about XUL that would survive today other than its layout model

Ignoring that XUL has a single implementation and for the most part a single application suite actually using it (not 100% true but very close), I'm not sure what there was to blow.

OTOH I remember some custom XUL apps of yesteryear, and they were always pretty nice to use. Does Firefox have any XUL left? I know there have been ideas to rip it out for a very long time.