When you say you got an access denied error, do you mean the server sent a 403 response?

If you compare the requests in the respective Network panels of the Firefox and Chrome dev tools, can you see any differences between the requests (headers, parameters, cookies, etc.)?

Thanks for your reply.

I'm using File.Create method from Microsoft .net framework to create or overwrite uploaded file in a path. (https://docs.microsoft.com/en-us/dotnet/api/system.io.file.create?view=netframework-4.7) While calling that method it returns: "Access to the path '\\\\somewhere' is denied." with no more details. (just in Firefox)

As the method's document, it would raise an error because of:

1:System.UnauthorizedAccessException: The caller does not have the required permission.-or- path specified a file that is read-only.

2:System.ArgumentException: path is a zero-length string, contains only white space, or contains one or more invalid characters as defined by System.IO.Path.InvalidPathChars.

3:System.ArgumentNullException: path is null.

4:System.IO.PathTooLongException:The specified path, file name, or both exceed the system-defined maximum length. For example, on Windows-based platforms, paths must be less than 248 characters, and file names must be less than 260 characters.

5:System.IO.DirectoryNotFoundException:The specified path is invalid (for example, it is on an unmapped drive).

6:System.IO.IOException: An I/O error occurred while creating the file.

7:System.NotSupportedException: path is in an invalid format.

So it seems the first one happens while creating the file and I catch the error and raise a custom error to the client (internal server error -500) then I do not have a real http statue code (because the method does not return any details)

Thanks,

Okay, the problem is on the server side. Why would it work differently in different browsers? My guess is that some header or parameter doesn't match was your ASP.net code expects, so please compare the requests as I suggested before.