clearInterval() is not stopping setInterval() – Firefox Extension Development-Collection of common programming errors

I am working on a modification of tamper data that will allow me to send the HTTP request/responses it observes to a server. So far, that functionality has been implemented correctly. The next step is to automate this process, and I wish to use a toolbarmenu button of type ‘checkbox’ to toggle this functionality on and off.

So far I have this bit of code in the .XUL:

And this function in the main driver of my extension:

toggleTimer : function() {
 var checked = document.getElementById('tamper.autosend').checked;

 var consoleService = Components.classes["@mozilla.org/consoleservice;1"].getService(Components.interfaces.nsIConsoleService);

 consoleService.logStringMessage(checked);

 if (checked) {
        var interval = window.setInterval(function(thisObj) { thisObj.sendResults(true); }, 1000, this);
 }

 else {
        window.clearInterval(interval);
 }
}

Using the consoleService I see that the value of ‘checked’ is indeed correct. I believe the problem lies with how I am calling clearInterval, but I’m not exactly sure how to remedy it.

Any help is greatly appreciated!