This includes the entire Servo team which was working on its next generation web engine that was supposed to be Firefox's ticket to staying afloat in the future. Servo also popularized the Rust language afaik
Aside from Servo, they also axed the entire threat management team, because why would a browser need threat detection and incident response, amirite?
Relevant links:
https://nitter.snopyta.org/directhex/status/1293352458308198401
https://nitter.snopyta.org/MichalPurzynski/status/1293220570885062657
https://news.ycombinator.com/item?id=24120336
https://news.ycombinator.com/item?id=24128865
didn't think anyone would use this kinda marketing speak after silicon valley satirized it