The web console and JavaScript debugger do not sanitize all output that can be hyperlinked. Both will display "chrome:" links as active, clickable hyperlinks in their output. Web sites should not be able to directly link to internal chrome pages. Additionally, the JavaScript debugger will display "javascript:" links, which users could be tricked into clicking by malicious sites. This vulnerability affects Firefox < 60.
https://www.mozilla.org/security/advisories/mfsa2018-11/
https://usn.ubuntu.com/3645-1/
https://bugzilla.mozilla.org/show_bug.cgi?id=1447969