I don't think the Firefox OS team was ever bigger than maybe 100 people at the absolute most, and I feel like it was closer to half of that. Admittedly it's been over a decade since I left, so my recollection could be wrong, but it was never "most of the resources" by any metric.

It was a tiny percentage of the overall staff; I traveled to the Toronto office to work with some of the graphics devs (the area I primarily worked in) and the floor we were on easily had 200 people in that one -- relatively small -- location.

B2G/FFOS gets a lot of well-deserved hate -- I quit after a year -- but its impact has been wildly blown out of proportion.