HTTS request using XMLHttpRequest

I am experimenting with Chrome Plugin programs. Recently when I fired a HTTPS request using XmlHTTPRequest from a HTTPS page using the plugin, it gives me this error:

Mixed Content: The page at 'proto://www.xyz.com/pathtosomething' was loaded over HTTPS, but requested an insecure XMLHttpRequest endpoint 'proto://www.abc.com/pathtosomething'. This request has been blocked; the content must be served over HTTPS.

(Note protocol -proto is https for the first website and http for the second)

The abc link is hardcoded to use HTTPS but when the plugin triggers the request, it gets converted to HTTP. Where am I going wrong?