Can't log in to Thunderbird add-ons account in Thunderbird

[Pixelcode]

I can't log in to my Thunderbird add-on account in Thunderbird. I have tried the following:

Logging in via browser

1. Open https://addons.thunderbird.net in Thunderbird.
2. Click on “log in” in the top right.
3. Firefox is opened.
4. Enter your credentials.
5. Still in Firefox, https://addons.thunderbird.net tells you: “Your log-in has failed. Please try again. Do you need help?” You are not logged in in Thunderbird.

Logging in inside Thunderbird

1. Open https://addons.thunderbird.net in Thunderbird.
2. Go to any add-on.
3. Click on the “Write a review” button.
4. https://accounts.firefox.com/authorization is opened in Thunderbird, but it only displays a blank page, so that you cannot log in.

What am I doing wrong?