Browsers enable you to define a user defined protocol handlers (e.g., moomoo://someplace.com?foo=1).
Which browsers enable you to POST to a user defined protocol?
<form action="moomoo://someplace.com" method="POST">
<input type="text" name="foo" value="1">
</form>
I would say 'none', because what you are asking doesn't make contextual sense.
POST is a part of HTTP, so the browser wouldn't know what you wanted it to do when you told it to 'POST' to some other protocol. In doesn't have the back-end capability to know what format the request messgae should be in, unless that format is identical to HTTP, in which case, why are you not just using HTTP?
Browsers can handle protocols other than the built-in ones, such as telnet:// links, but in these cases they always sub the task out to an external program - with telnet:// on Windows, telnet.exe is started with arguments to tell it what to connect to.
I would say what you need to do is look at whether your new protocol is actually necessary - could you do the same thing over HTTP, work out exactly what you want the browser to do from a TCP/IP point of view. If you conclude that you do need a new protocol, you will have to write a program that the browser can hand off requests for your protocol to, and register it within the browser, so that the browser know what to do with it - how you actually do this depends on the browser and the OS.
If you want to give more information about exactly what your trying to achieve with your new protocol, I would be happy to see what I can come up with...
