A recent update to an ad block filter list now allows the uBlock Origin extension to block most of the known sites that perform port scans of your local Windows computer. eBay is using fraud detection scripts that port scan a visitor’s computer for Windows remote access programs. The port scans are being conducted by the LexisNexis’ ThreatMetrix product and will use WebSockets to port scan the computer for specific ports on the 127.0.0.1 (localhost) address.
Source: https://www.bleepingcomputer.com/news/security/ublock-origin-ad-blocker-now-blocks-port-scans-on-most-sites/