Only 'save multiple images' (by pressing ALT) works for me. Debug shows a warning related to the manifest. Maybe that's the cause for the other features not to work properly ...
Update: Issues fixed in 1.5.2 - thx!

I am unable to get this operating with Firefox browser.

Thank you so much for the new update. It's working very well. All problems solved.

Починили авторизацию с 2FA, меняю оценку на отлично.

Unable to login with correct credentials, never prompts for 2FA details. Useless.

not worth the effort. still doesn´t work (jun2021).

I like pCloud but this addon doesn't seem to work at all in Firefox. It doesn't even appear in the right-click menu.

Europe Union zone not supported and I can't login into account via username and password

Not possbile to login ...
(user/password not working BUT only for this Firefox extension : user/password perfectly works for site on web and for application on Android)

cannot log in with correct email and password...

Unable to log in with login/password. (EU Datacenter)

Same issue as everyone else. Unable to log in with correct username & password. As a new user to pCloud I am not impressed with the lack of interest to resolve this issue

L'ancien Addon était largement meilleur et plus pratique. De plus impossible de rester enregistré.

Does not allow login if your datacenter is EU region. pCloud support is not committed to resolving this anytime soon. Also, you need to pay $20 to change the datacenter region to US and it will render your account unusable for a few days. pCloud does not commit on how long will the process take.

Can't login with correct login information. I'm starting to doubt pCloud's commitment to fix this, since old reviews state the same.

Same with alot of people the last few months. Can NOT log-in with my account information. I even logged out of the website itself and logged back in with no problems, but cannot log into the app extension in Firefox.

Unable to log in with login/password. (EU Datacenter)

Wrong username or password message.
It's working great through other means though!