@mcc I’m not sure. They said something in 2017 about planning to excise XUL (which, yes, 💯). But I can’t find a release since then with a formal declaration that the work has been done.
(I’m not an active SeaMonkey user myself, so all I know is what I read on their web site.)
@jalefkowit @mcc I do still kinda have some nostalgia for Composer. The whole "suite" idea gets a bit of a bad rap, I think; MS Office (and, heck, iWork) is a "suite" and nobody has problems with that, because it still presents the elementts of its suite as normal applications and not as a single fused block of functionality that is inexplicably built as its own launcher.