For those who have issues with constant login screen. All you have to do is:

1. go to Settings -> Privacy and Security
2. scroll to Cookies and Site Data
3. click Manage Exceptions
4. in field Address of website enter https://tagpacker.com
5. click button Allow
6. click button Save Changes

I guess Tagpacker should put this guide in plugin description.

I've been using tagpacker and the add-on for some time now. It is intuitive to use, comes with nice features (e.g., adding pictures to links, getting link recommendations etc.) and organizing by tags (instead of folders) makes organizing content very flexible. I haven't used any other bookmarking services for comparison but tagpacker provides all I need.