I have found many extensions that require a login to a 3rd party service don't seem to remember the logged-in state. Some examples:
Pocket-based extensions:
https://addons.mozilla.org/en-US/firefox/addon/in-my-pocket/?utm_source=addons.mozilla.org&utm_medium=referral&utm_content=search
https://chrome.google.com/webstore/detail/save-to-pocket/niloccemoadcdkdjlinkgdfekeahmflj
Also, the bookmarklet from Pocket suffers the same problem == when you use it it asks you to login; once you do log in, you get the same "please log in" the next time you use it.
I've noticed the same issue for Instapaper and Raindrop.