This extension is being flagged by windows defender as a "severe" threat malware. Why?

Works great, very light! Some sites don't like it, no problems!

schon lange auf so etwas gewartet

It is kinda laggy sometimes(it took 4 GIGABYTES of ram once, firefox with all my tabs rarely takes more than 1 gb), thus a four star rating. Maybe it is all ad-blockers thing, a good choice either way. And you can pretty easily customise what to block(even non-ads), which is pretty useful