It is unclear if the firmware update did anything that affected the noise cancelling feature, but unfortunately, since there is no changelog, no one really knows except for Apple, and the company has been keeping mum ever since. To make matters worse, firmware updates aren’t something that users can opt not to participate in.
The firmware update for the AirPods happens entirely in the background without users knowing when it takes place. In a way, this is good as it ensures that the earphones are constantly updated, but at the same time, it’s bad because it can lead to situations like this where users do not have an option to not install the latest update.
That being said, as The Verge points out, Apple is not alone in this. In the past, Bose and Sony customers have also similarly complained that noise cancelling on their headphones was affected following firmware updates. It is unclear if this is actually happening or if it is merely perception.