I think we're at the point where we need to ask, how the fsck supposedly "open browser" prohibits their own users from installing extensions they want to install? I mean, I get signing - if you want signing, you can use it. I even get the config option for enterprise setups, maybe - so if an org wants to standardize on Firefox and prohibit workers from installing unsigned extensions - fine. But when it comes to my own install, that's just bullshit.
It's a trade off between security for normies and power for technical users. I disagreed at the time (as an addon author) yet have come around to agreeing with the choice.