Setting aside that the problem with AV had nothing to do with Apple, for the most part nobody was working at either of those offices over the summer (2020, remember?). Also, which of Apple's 130+ Silicon Valley offices are you going to go to, and who do you ask for when you get there?
It sounds like this was an issue with an independent antivirus vendor, not Apple.
I'd imagine that security and the front desk are going to prevent anyone from entering to meet with specific teams or individuals without an appointment.
If you knew someone and had scheduled time with them, then yeah I'm sure you could hoverboard your way over.
But Apple and Mozilla headquarters are 5 miles apart (roughly). Couldn't you just walk/drive/scoot/fly/what ever over and talk to someone?