CVE-2021-23986

A malicious extension with the ‘search’ permission could have installed a
new search engine whose favicon referenced a cross-origin URL. The response
to this cross-origin request could have been read by the extension,
allowing a same-origin policy bypass by the extension, which should not
have cross-origin permissions. This cross-origin request was made without
cookies, so the sensitive information disclosed by the violation was
limited to local-network resources or resources that perform IP-based
authentication. This vulnerability affects Firefox < 87.

Notes