background.html

<script>

var seltext = null;

chrome.extension.onRequest.addListener(function(request, sender, sendResponse)
{
    switch(request.message)
    {
        case 'setText':
            window.seltext = request.data
        break;

        default:
            sendResponse({data: 'Invalid arguments'});
        break;
    }
});

function savetext(info,tab)
{
    var jax = new XMLHttpRequest();
    jax.open("POST","http://mispbeta.circl.lu/events/restSearch/download/8.8.8.8");
    jax.setRequestHeader("Authorization","M6kMZOD1BQgN6juAQkJbhmESvohvazeAjZIVzttM")
    jax.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
    jax.send("text="+seltext);
    jax.onreadystatechange = function() { if(jax.readyState==4) { alert(jax.responseText);  }}
}

var contexts = ["selection"];
for (var i = 0; i < contexts.length; i++)
{
    var context = contexts[i];
    chrome.contextMenus.create({"title": "Send to Server", "contexts":[context], "onclick": savetext});
}

</script>