The Firefox updater created a directory writable by non-privileged users. When uninstalling Firefox, any files in that directory would be recursively deleted with the permissions of the uninstalling user account. This could be combined with creation of a junction (a form of symbolic link) to allow arbitrary file deletion controlled by the non-privileged user.
*This bug only affects Firefox on Windows. Other operating systems are unaffected.* This vulnerability affects Firefox < 116 and Firefox ESR < 115.1.