Nginx cut-off Content-Type header in responce id http status is 204

Question

I have following configuration nginx server that proxy requests to tomcat server:

location /api/ {
    proxy_pass http://127.0.0.1:8080/;
    proxy_read_timeout 90;
}

This works fine, but in firefox we have issue like in this: Firefox error 'no element found'

Why nginx cut-off content-type header, and how to prevent him from doing it?