rootの後、ダウンロードはできません -- samsung-galaxy-s-5 フィールド と file-permissions フィールド android 関連 問題

I rooted my Samsung Galaxy S5 (Android 5.0, SM G900F) recently with Odin. While I rooted it, I had Kingroot installed. Since Kingroot took over the root management, I'm not able to download files with 3rd party apps (like my browser or whatsapp). I already tried to replace Kingroot with SuperSU, but the script which seems to be the only way to do that didn't work for me. For me it looks like the apps didn't have the permission to write to the internal storage. For some reason downloading apps from the Google Play Store works. I downloaded "Root Browser" and it shows me, that my whole /storage/emulated/0/ is owned by root:root and has rwxrwx--x permissions (the subdirectories too) what seems a little bit strange for me (is that normal?), but I'm not able to change them (Root Browser says that you can't change permissions on some file systems). I already searched for this problem, but I didn't find anything. I hope someone can help me with this.