From #33534: Attempts to navigate to an unknown protocol using methods such as location.href or <meta http-equiv="refresh"> are now blocked. We should verify that our patch for #19273 and related bugs is still effective and that the new behavior does not allow web pages to more easily detect whether a protocol handler is installed. https://bugzilla.mozilla.org/show_bug.cgi?id=1528305 \ "Behavior on meta and location.href redirects to an unknown protocol can break pages." https://www.fxsitecompat.dev/en-CA/docs/2020/navigation-to-unknown-protocol-will-be-blocked/