By using the reflected URL in some special resource URIs, such as chrome:, it is possible to inject stylesheets and bypass Content Security Policy (CSP). This vulnerability affects Firefox < 63.
https://www.mozilla.org/security/advisories/mfsa2018-26/
https://usn.ubuntu.com/3801-1/
https://bugzilla.mozilla.org/show_bug.cgi?id=1488061
https://bugzilla.mozilla.org/show_bug.cgi?id=1460538