Spoofing Attack

Thunderbird and Firefox are vulnerable to spoofing attack. The vulnerability exists due to a misuse of a race in the notification code allowing an attacker to forcefully hide the notification for pages that had received full screen and pointer lock access...

Mozilla: Missing fullscreen and pointer lock notification when requesting both

The Mozilla Foundation Security Advisory describes this flaw as: By misusing a race in our notification code, an attacker could have forcefully hidden the notification for pages that had received full screen and pointer lock access, which could have been used for spoofing attacks...