xcancel.com is down. The new version of the plugin points at another nitter instance (https://nitter.kareem.one ).
(In the future it would be great to make it possible to let you specify any arbitrary url, but that will require a bit more work so it will be done later (perhaps (if I have time to work on it)))

ToXCancel now intercept the queries to x.com or twitter.com and redirect it to xcancel.com before they are performed (instead of first querying x.com and then quickly redirecting to xcancel.com). This hence avoids completely performing a query against x.com or twitter.com

assessed compatibility with firefox-mobile

fix handling of urls with query string