Where the browser gives no sender.origin (Firefox before 126), the background credited a page's request to the tab's page, so a frame from another site counted as the site embedding it, and with no tab it used an origin the page wrote into the message. It now uses the origin of sender.url, the frame that sent the message, and refuses the request with code 4100 when the browser gives neither. The content script no longer writes an origin into the message. Model: opus-5-5