Mozilla laid off 250 employees. Some of them very important for the core feature "development tools", that keeps quite some users with advanced IT-knowlegde around, and the threat-management (hunts down of security issues). Those people will seek new jobs and I can't imagine them returning later on, so that's some good knowledge gone.
Also let me honorably mention MDN.
I also read somewhere, that 250 is around 25% of their staff, and many people aren't taking that Corona-reason. Maybe google cut them their budget, because they said they do make less money now with their advertisement, but maybe they (google/Mozilla management) want to shrink Mozilla even further. Mozilla beside: This is taking a horrible turn for Firefox and we might lose something very valuable. The best alternative to a google based web browser engine.
Trident going down, wasn't a good thing either. No matter alternatives like Brave (I can't write anything bad about it, as I didn't used it til now), if they are chromium based, in the end google has control over them to a good degree. How much of the source code of Blink is provided by google and what would happen, if they decide to flood it with new "better/advanced/more secure" code? Ain't they able to steer the project any direction they want? (Android is also an open source, free OS, but you can't tell me google isn't adding new "features" all the time. They own it.) Other players are also part of the gig, namely Samsung and Intel. I don't know about you, but Samsung, while providing very good products, didn't leave a good impression on me regarding "free-/fairness". They are hardcore players, when it comes down to their own interests. I fear some "well meant" feature will land in Blink as soon as Gecko is gone. (Its successor Servo also seems to be a victim of the recent Mozilla lay-offs.) Color me surprised, if no-tracking brave somehow manages to brave those tides of change.