I've noticed for some time that Munchkin visitWebPage pixel is being blocked by the latest version of Firefox with the following warning:
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://253-xld-026.mktoresp.com/webevents/visitWebPage
This doesn't seem to impact lead tracking, as the "Visit Web Page" event is still showing up in the lead's Activity Log, but it is registering as an error on the page, which bothers me. Without doing too much troubleshooting, I'd guess the issue is a stems from the tracking pixel response trying to set a cookie, but not sending the "access-control-allow-credentials" header, or the request not using "with-credentials", or something similar to that...