It should also be noted that Mozilla has the smallest security team of all major web browsers. Apple's Safari and Google's Chrome security teams are an order of magnitude larger than Mozilla's team.
Unfortunately that tweet has been misinterpreted and has grown into a false narrative.
This is what I know about what happened there:
There were two enterprise IT teams with similar duties but different purviews. When management was deciding on layoffs, they decided to unify those two teams. Unfortunately that meant that there were redundancies.
My heart goes out to those who lost their jobs, and they have every right to be upset.
But the inferences being made as a result of that tweet just aren’t true: this notion that all security teams were wiped out is false. And there are now others assigned to threat management.
Furthermore, the security teams that work on Gecko and Firefox were left mostly if not entirely intact.
I work on security hardening for Gecko on Android, and I’m still here. So is our entire hardening/sandboxing team: https://twitter.com/gcpascutto/status/1293519587967983616
TL;DR: Don’t base your understanding of an organization’s capabilities off of one tweet.
Gian-Carlo is amazing by the way and gets way too little visibility for the important work he is doing.