Thanks, didn't know that.
https://files.minecraftforge.net/maven/net/minecraftforge/fernflower/
Since I can't find "forgeflower" on the maven I'm assuming this is actually it, even though that's not what its called. Is that correct? It decompiled my mod with the exact same problems as FernFlower, so I'm not really sure. I tried to read the 16 entries in FernFlower-Patches but didn't understand them to a degree where I could actually tell if my problems are adressed by ForgeFlower.