In Reader View SameSite cookie protections are not checked on exiting. This allows for a payload to be triggered when Reader View is exited if loaded by a malicious site while Reader mode is active, bypassing CSRF protections. This vulnerability affects Firefox < 61.
https://bugzilla.mozilla.org/show_bug.cgi?id=1456652
https://security.gentoo.org/glsa/201810-01
https://usn.ubuntu.com/3705-1/