A vulnerable object in the browser’s core and HTML handling layer can be freed before all references are released, creating a use‑after‑free scenario. If exploited, an attacker could trigger a crash or potentially execute arbitrary code with the privileges of the browser process. The weakness stems from improper memory management in the DOM parsing engine, classifying it as a classic use‑after‑free flaw.

Mozilla Firefox and Thunderbird users running any release prior to 155 or the ESR build before 153.2 are affected. The issue exists in the core DOM and HTML components, and is fixed in Firefox 155 and Firefox ESR 153.2, and in Thunderbird 155 and Thunderbird ESR 153.2.

Based on the description, it is inferred that an attacker could exploit the flaw via crafted web content or malicious extensions, implying a remote attack vector that requires the victim to visit a specialized page or run a compromised add‑on. The vulnerability has a CVSS score of 5.4, indicating medium severity. No EPSS score is available and the vulnerability is not listed in the CISA KEV catalog, suggesting limited publicly known exploits, but the moderate severity warrants prompt action.