A malicious extension could have called <code>browser.identity.launchWebAuthFlow</code>, controlling the redirect_uri, and through the Promise returned, obtain the Auth code and gain access to the user's account at the service provider. This vulnerability affects Firefox < 75.
75.0+build3-0ubuntu0.16.04.175.0+build3-0ubuntu0.18.04.138.8.0~repack1-0ubuntu138.8.0~repack1-0ubuntu338.8.0~repack1-0ubuntu452.3.1-0ubuntu352.3.1-7fakesync152.8.1-0ubuntu0.18.04.152.9.1-0ubuntu0.18.04.175.0+build3-0ubuntu152.9.1-1build152.9.1-1ubuntu368.5.0-1~fakesync68.5.0-2~fakesync68.6.0-168.6.0-1ubuntu1Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:HI:HA:HCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H