@christophehenry They did work on both of those in Emerging Technologies (which was disbanded and most folks laid off in 2020).
I think IoT was seldom more than two people, usually one, and maybe some supporting folks around the web standards.
Hubs (a VR meeting space) was a bit larger, and had some external funding. Apparently it's spun off: https://hubsfoundation.org/ (it's always hard to know how successful these things are though)
In cases like these Mozilla usually hoped something would eventually spin off. These were never going to be a new direction for Mozilla or Firefox.