First thought: "What? Why would I ever allow some third party plugin to get on my browser and take control over my passwords?"
Second thought: "Some wise professionals suggested it is a good idea, I should look into it."
I have installed the plugin in a kind of isolation mode (I don't use FireFox for other things than testing, so I could use that).
Third thought: "What an ugly and unfriendly user interface?!"
The password got shared with me, I received it via LastPass plugin in FireFox. It worked to access the web app I was about to test. I thought I would have a look at that password. The user who shared it blocked it from viewing it: "This is a shared site. You are not permitted to view the password." Kind of good idea. But...
Next thought: "Once something is in my browser put into a form field it means it gets send out to the web, hence I should be able to see it if I want, because it is just there!"
So much to block viewing shared passwords.
Anyway, thought after thought I proved to myself that using any third party SaaS for sharing, keeping passwords is a NO.