The new UI is bad, but that's up to one's taste and needs, so we can skip it.
But UX? Absolutely horrible!
Why would you decide it's cool to have all of the passwords show always? It slows down the extension (if the user needs to enter the extension).
I won't repeat the rest of the user feedback others have already written.
You've seen on Chrome that users absolutely hate the new look and functionality.
You saw on Reddit people were completely loosing their minds how bad all of this is.
And you're like: "Let's destroy our rating on Firefox as well".
I understand this went through a beta phase - and clearly you had the wrong people provide you with feedback - or you didn't invest time in getting the right people test this.
I'm working in IT, and I can tell you none of this has been handled properly - whoever was in charge of this change has completely failed at their job.
Rolling out these changes gradually? Yes
Seeing all of the feedback and stopping the rollout until you figure out how to deal with a huge backlash? Nope, let's ignore it, roll it out to everyone and then say we're going to give you options.
Terrible strategy - this is exactly how you loose clients.