Firefox behaved slightly differently for already known resources when loading CSS resources involving CSS variables. This could have been used to probe the browser history. This vulnerability affects Thunderbird < 91.9, Firefox ESR < 91.9, and Firefox < 100.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Firefox | Mozilla | * | 100.0 (excluding) |
| Firefox_esr | Mozilla | * | 91.9 (excluding) |
| Thunderbird | Mozilla | * | 91.9 (excluding) |