How do I POST to a web page using Firebug?
Firefox 27 (maybe earlier versions too, never checked) has built-in developer tools to modify and resend requests. If you don't have Firebug installed, the console is available by pressing the F12 key. If Firebug is installed, press Ctrl+Shift+K
instead.
AFAIK Firebug can't do this. However, there is a very useful Firefox extension, in the spirit of Firebug, called Tamper Data. This should be able to do what you want.
It allows you to monitor each request made by the browser, and you can turn on an option that allows you to look at, and edit, every single request before it gets sent.
I know this is an old question, but I recently stumbled upon the same problem and wanted to share the method I am using.
Assuming the web site you want to POST to has a form with method="POST" (a very likely scenario), you can use Firebug's JavaScript command line to programmatically submit a POST request. Just click the "Show Command Line" icon in Firebug and enter something like this in the narrow text box at the very bottom of the window:
document.forms[0].submit()
Maybe this helps someone.
Another powerful Firefox plugin to perform post request and some more features is the Hackbar.