High
Mozilla Firefox could allow a remote attacker to execute arbitrary code on the system, caused by an error when opening an extension-less download. By persuading a victim to visit a specially-crafted Web site, a remote attacker could exploit this vulnerability to launch an executable and execute arbitrary code on the vulnerable system or cause a denial of service.
Mozilla
Refer to Mozilla Foundation Security Advisory 2020-54 for patch, upgrade or suggested workaround information.
https://www.mozilla.org/en-US/security/advisories/mfsa2020-54/