How to send manually a HTTP POST request... and get back the actual website

I am debugging a form in a web application, and I need to disable Javascript to see how the server will respond... except that the form's "Submit" button is wired to a Javascript function which submits it by calling the POST URL. How can I trigger this HTTP POST call manually?

I have looked at browser add-ons like RESTClient or REST Easy... but they seem to be oriented to debugging REST apps, and thus, only return the raw HTML, which in my case has hundreds of lines of scripts, headers, etc., and it's hard to wade through all of that cruft to see the actual response given by the server. Is there any way to do that and get back the actual rendered web page, just as if it was a client submitting the form? (only, you know, without executing the Javascript first).