Hello, thank you for trying out my extension.
eBay recently changed their card layout code, I have released a new version 0.2.1 of this extension last week, that I have confirmed is working on eBay.de.

You may have to do these steps listed in this screenshot: https://imgur.com/kTV6zkd
1. Make sure you have version 0.2.1 installed (you can see version # at bottom of extension details page)
2 & 3. Add ebay.de domain in extension settings (this was the problem when I tried it out, extension will not work without this)
4. Allow extension to run on ebay.de, when asked by Firefox.

If you have an ebay.de page open, refresh your page with Ctrl+F5 before you check.

Here is an animated GIF showing the extension working on ebay.de: https://imgur.com/q8ftXYM

Would love to get more details/screenshots from you, if it still does not work for you.