If you install this addon and open settings, it will open the following - remotely hosted - URL: ttps://feeder.co/settings/feeds?ctx=extension where you can manage your feeds (local configuration is not possible)
This remotely hosted website somehow magically knows all feeds you have added (even though I have not registered or anything else). This is quite surprising because I installed this program on my local machine and expected that it operates locally, not remotely. But this addon must have transferred my personal data to the feeder company (the feeds I have added etc.) so that they know which ones to show when feeder addon redirects me to their website. From the Cambridge Analytica scandal we know that knowing someones website preferences tells you much about the personality - hence it is personal data.

The point is that I never told / allowed feeder addon to transfer all my personal data to the feeder website. And if you look in the privacy policy you won't find any information about how this data stored and used. Is this GDPR complaint? Because this addon has the following functionality: Show me feeds. It is not necessary that those feeds are transferred to feeder.co. Because they could also program an offline, locally stored setting page. Hence, the user must be asked if he wants to allow this extra, unnecessary data transfer. But he isn't... I'd recommend that you fix this soon because GDPR finally includes real, substantial penalties...