Ygtjki

I have nginx (1.10.3-1+deb9u2) on Debian 9.6. I have installed php7.1-fpm from external repository (sury.org). I have simple php file executing phpinfo() function (and nothing more), simply to see if everything works. Now for the funny part. I have it on embedded device with "normal" ethernet interface - if I connect from my PC using this interface I got expected results. But when I connect via USB, so that there is RNDIS-like (or RNDIS, I'm not sure) network interface created, things do not work as expected, that is if I connect using Firefox, I see a dialog asking me where I want to save file - which is exactly the file that should be executed by nginx + fpm combo. But when I connect using Chrome, I get expected result, so standard phpinfo()-generated page.

I believe that configuration is absolutely standard Nginx stuff. Does anyone has any idea how could that happen? If behavior were different depending on the interface that I connect on, it would be pretty obvious information that for some reason Nginx refuses to execute my request using php module. But it depends on the browser that I use and this is bewildering to be honest.

I checked how connections are made in both Fireox and Chrome using developer tools and it seems that they are basically identical, in addition there are no redirections, so that's not it. I haven't tried wget/curl yet and I can't do it now, but no matter what the result will be this is still inacceptable.

Any ideas? No matter how wild they are?

EDIT (configuration):

I've been able to confirm nginx configuration. It is as follows:

user www-data;
worker_processes auto;
pid /run/nginx.pid;
include /etc/nginx/modules-enabled/*.conf;
events 
 worker_connections 768;

http 
 sendfile on;
 tcp_nopush on;
 tcp_nodelay on;
 keepalive_timeout 65;
 types_hash_max_size 2048;
 include /etc/nginx/mime.types;
 default_type application/octet-stream;
 ssl_protocols TLSv1 TLSv1.1 TLSv1.2; # Dropping SSLv3, ref: POODLE
 ssl_prefer_server_ciphers on;
 access_log /var/log/nginx/access.log;
 error_log /var/log/nginx/error.log;
 gzip on;
 gzip_disable "msie6";
 include /etc/nginx/conf.d/*.conf;
 include /etc/nginx/sites-enabled/*;

load_module modules/ngx_http_auth_pam_module.so;
load_module modules/ngx_http_dav_ext_module.so;
load_module modules/ngx_http_echo_module.so;
load_module modules/ngx_http_geoip_module.so;
load_module modules/ngx_http_image_filter_module.so;
load_module modules/ngx_http_subs_filter_module.so;
load_module modules/ngx_http_upstream_fair_module.so;
load_module modules/ngx_http_xslt_filter_module.so;
load_module modules/ngx_mail_module.so;
load_module modules/ngx_stream_module.so;
types 
 text/html html htm shtml;
 text/css css;
 text/xml xml;
 image/gif gif;
 image/jpeg jpeg jpg;
 application/javascript js;
 application/atom+xml atom;
 application/rss+xml rss;
 text/mathml mml;
 text/plain txt;
 text/vnd.sun.j2me.app-descriptor jad;
 text/vnd.wap.wml wml;
 text/x-component htc;
 image/png png;
 image/tiff tif tiff;
 image/vnd.wap.wbmp wbmp;
 image/x-icon ico;
 image/x-jng jng;
 image/x-ms-bmp bmp;
 image/svg+xml svg svgz;
 image/webp webp;
 application/font-woff woff;
 application/java-archive jar war ear;
 application/json json;
 application/mac-binhex40 hqx;
 application/msword doc;
 application/pdf pdf;
 application/postscript ps eps ai;
 application/rtf rtf;
 application/vnd.apple.mpegurl m3u8;
 application/vnd.ms-excel xls;
 application/vnd.ms-fontobject eot;
 application/vnd.ms-powerpoint ppt;
 application/vnd.wap.wmlc wmlc;
 application/vnd.google-earth.kml+xml kml;
 application/vnd.google-earth.kmz kmz;
 application/x-7z-compressed 7z;
 application/x-cocoa cco;
 application/x-java-archive-diff jardiff;
 application/x-java-jnlp-file jnlp;
 application/x-makeself run;
 application/x-perl pl pm;
 application/x-pilot prc pdb;
 application/x-rar-compressed rar;
 application/x-redhat-package-manager rpm;
 application/x-sea sea;
 application/x-shockwave-flash swf;
 application/x-stuffit sit;
 application/x-tcl tcl tk;
 application/x-x509-ca-cert der pem crt;
 application/x-xpinstall xpi;
 application/xhtml+xml xhtml;
 application/xspf+xml xspf;
 application/zip zip;
 application/octet-stream bin exe dll;
 application/octet-stream deb;
 application/octet-stream dmg;
 application/octet-stream iso img;
 application/octet-stream msi msp msm;
 application/vnd.openxmlformats-officedocument.wordprocessingml.document docx;
 application/vnd.openxmlformats-officedocument.spreadsheetml.sheet xlsx;
 application/vnd.openxmlformats-officedocument.presentationml.presentation pptx;
 audio/midi mid midi kar;
 audio/mpeg mp3;
 audio/ogg ogg;
 audio/x-m4a m4a;
 audio/x-realaudio ra;
 video/3gpp 3gpp 3gp;
 video/mp2t ts;
 video/mp4 mp4;
 video/mpeg mpeg mpg;
 video/quicktime mov;
 video/webm webm;
 video/x-flv flv;
 video/x-m4v m4v;
 video/x-mng mng;
 video/x-ms-asf asx asf;
 video/x-ms-wmv wmv;
 video/x-msvideo avi;

server 
 listen 80 default_server;
 listen [::]:80 default_server;
 root /var/www/html;
 index index.php index.html index.htm index.nginx-debian.html index.php;
 server_name beaglebone;
 location / 
 try_files $uri $uri/ =404;
 
 location ~ .php$ 
 include snippets/fastcgi-php.conf;
 fastcgi_pass unix:/var/run/php/php7.1-fpm.sock;
 
 location ~ ^/.*.html$ 
 include snippets/fastcgi-php.conf;
 fastcgi_pass unix:/var/run/php/php7.1-fpm.sock;
 

fastcgi_split_path_info ^(.+.php)(/.+)$;
try_files $fastcgi_script_name =404;
set $path_info $fastcgi_path_info;
fastcgi_param PATH_INFO $path_info;
fastcgi_index index.php;
include fastcgi.conf;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_param QUERY_STRING $query_string;
fastcgi_param REQUEST_METHOD $request_method;
fastcgi_param CONTENT_TYPE $content_type;
fastcgi_param CONTENT_LENGTH $content_length;
fastcgi_param SCRIPT_NAME $fastcgi_script_name;
fastcgi_param REQUEST_URI $request_uri;
fastcgi_param DOCUMENT_URI $document_uri;
fastcgi_param DOCUMENT_ROOT $document_root;
fastcgi_param SERVER_PROTOCOL $server_protocol;
fastcgi_param REQUEST_SCHEME $scheme;
fastcgi_param HTTPS $https if_not_empty;
fastcgi_param GATEWAY_INTERFACE CGI/1.1;
fastcgi_param SERVER_SOFTWARE nginx/$nginx_version;
fastcgi_param REMOTE_ADDR $remote_addr;
fastcgi_param REMOTE_PORT $remote_port;
fastcgi_param SERVER_ADDR $server_addr;
fastcgi_param SERVER_PORT $server_port;
fastcgi_param SERVER_NAME $server_name;
fastcgi_param REDIRECT_STATUS 200;
fastcgi_split_path_info ^(.+.php)(/.+)$;
try_files $fastcgi_script_name =404;
set $path_info $fastcgi_path_info;
fastcgi_param PATH_INFO $path_info;
fastcgi_index index.php;
include fastcgi.conf;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_param QUERY_STRING $query_string;
fastcgi_param REQUEST_METHOD $request_method;
fastcgi_param CONTENT_TYPE $content_type;
fastcgi_param CONTENT_LENGTH $content_length;
fastcgi_param SCRIPT_NAME $fastcgi_script_name;
fastcgi_param REQUEST_URI $request_uri;
fastcgi_param DOCUMENT_URI $document_uri;
fastcgi_param DOCUMENT_ROOT $document_root;
fastcgi_param SERVER_PROTOCOL $server_protocol;
fastcgi_param REQUEST_SCHEME $scheme;
fastcgi_param HTTPS $https if_not_empty;
fastcgi_param GATEWAY_INTERFACE CGI/1.1;
fastcgi_param SERVER_SOFTWARE nginx/$nginx_version;
fastcgi_param REMOTE_ADDR $remote_addr;
fastcgi_param REMOTE_PORT $remote_port;
fastcgi_param SERVER_ADDR $server_addr;
fastcgi_param SERVER_PORT $server_port;
fastcgi_param SERVER_NAME $server_name;
fastcgi_param REDIRECT_STATUS 200;

I thought that maybe there are two server blocks, but as you can see there is only one. What is strange is that when I connect using Firefox and nginx (?) serves file instead of executing it, there is nothing in /var/log/nginx/access.log.