When a new protocol handler is registered, the API accepts a title argument which can be used to mislead users about which domain is registering the new protocol. This may result in the user approving a protocol handler that they otherwise would not have. This vulnerability affects Firefox < 63. References: https://bugzilla.mozilla.org/show_bug.cgi?id=1490276 External References: https://www.mozilla.org/en-US/security/advisories/mfsa2018-26/#CVE-2018-12399