It’s impressive that they are able to fix them so quickly – one needs to imagine they get a non-trivial number of reports, and that some majority of them are junk. They have a good triage + repro + escalation system.
(https://www.fb.com/818902394790655)
They probably got a couple people working exclusively on bug bounty reports. I also have to say they did a great job changing communication channels from emails to tickets which show in /support/, it is way easier now. The downside is that you must have a Facebook account, not sure if it was needed before the change.