The user can review some information about access permissions but so many extensions make the same plea: "i know that my extension is using lots of permissions, but it's totally safe".
Much like Windows and Android, the endless alerts about permissions and confirmations, while perhaps holding real information, end up becoming little more than noise.
Combine that with a free-fire zone where apparently little moderation or pruning occurs... it's bad news waiting to happen.
(edit: I'm a Chrome user in addition to FF and I use a lot of extensions... they are super useful, but I have serious concerns about this)