If a site is loaded over a HTTPS connection but loads a favicon resource over HTTP, the mixed content warning is not displayed to users. This vulnerability affects Firefox < 63.
[
{
"product": "Firefox",
"vendor": "Mozilla",
"versions": [
{
"lessThan": "63",
"status": "affected",
"version": "unspecified",
"versionType": "custom"
}
]
}
]