They'd better have the best post mortum ever, possibly with someone being fired.
Or you fire the scapegoat because of a broken system that allowed one person to make a mistake?
That might seem rather extreme, but the fact that this situation was even possible was a consequence of a series of bad decisions over an extended period of time about the required behaviour of new versions of Firefox, combined with technical failures that betray fundamental weaknesses in the whole system design. Whoever was ultimately responsible for those failings demonstrably isn't competent to run something of this importance and should probably either implement immediate and dramatic changes to the relevant policies and technical details or consider their position. Anything less is surely going to damage trust, which is something Firefox can ill afford when it's already in danger of being reduced to a niche product rather than a mainstream browser.
But we're outsiders looking in and don't know what's going on at this point. That's why I used the qualifier "possibly." It's quite possibly it wasn't incompetence.
That's true, sort of. How often do you let people make huge mistakes before you decide that maybe they are just not apt for the position that they've been promoted to and Peter was right? Once? Twice? And unlimited amount, as long as it's never the exact same mistake?