It is in fact possible to send a HTTP Post directly from the address bar of many browsers, in order to call a particle.function by pasting this string after adding you own data:
data:text/html,<body onload="document.body.firstChild.submit()"><form method="post" action="https://api.particle.io/v1/devices/DEVICEID/FUNCTIONNAME"><input value="TOKEN" name="access_token"><input value="6" name="args">
Fill in DEVICEID, particle.function FUNCTIONNAME and your TOKEN. Also, in this example an argument is passed to the function (the number 6).