That's for non-public add-ons. If you submit a public add-on, even a minor update, it has to go through the AMO bureaucracy. I currently have an update that was uploaded on July 10, 2015, and is at queue position of 64 of 137. There are no code changes; it's just being updated because Mozilla changed their build system.
This seems to be part of Mozilla's effort to be more like the Apple and Google stores.
I wouldn't think Chrome Web store is full of Malware. Yes, it's not free of those, but the bad ones are quickly removed by both Chrome's policing, and users' flagging. That's how Mozilla should go forward. The problem with manual reviewing is, it depends on the 'volunteers' time availability, and a stupid Review system which is NOT FCFS. You are told you are 37th out of 150 in the queue, but you see that you either remain at that position while others are being approved, your queue position goes both up and down, and some times your add-on is instantly approved even when you are 100th in the queue. All this takes many days even if your users are waiting for a critical fix. This is the biggest turn off in uploading add-ons for Firefox.
You can sign the addons and distribute it on other channels. If you want to have it on AMO then it takes a while to review. The process is done by volunteers
This is one of the things which is frustrating about Mozilla.
I love that they stand for open protocols, free software and user privacy, but I don't love what they prioritize.
Reviewing extensions is critical to their user-experience.
If this really doesn't have an team of paid staffers, that's unfortunate.
This seems to be part of Mozilla's effort to be more like the Apple and Google stores.
Mozila AMO - Learn to embrace the pain.