How to open remote file URL (e.g. index.html) directly in browser?

I'm using WinSCP to manage files on my remote server.
I have an index.html file in my remote directory. I would like to right-click on it and choose an option like "Open in browser" (e.g. Firefox), so it opens the file's public URL directly.

I have already created a WinSCP extension for that.
The URL it opens is:
http://ftp.xxxx.com/txxxxx/xxxx/index.html
(because my session is logged in to ftp.xxxx.com)

But I actually want the URL to be:
http://xxxx.com/txxxxx/xxxx/index.html

I can't figure out how to change this behavior in the extension. Any idea how to fix it?

Thanks!