Mozilla released Firefox version 136.0.4 to address a critical security vulnerability, CVE-2025-2857, which could allow attackers to escape the browser's sandbox on Windows systems. This flaw, identified by developer Andrew McCreight, affects both standard and extended support releases of Firefox. Mozilla patched this issue in Firefox 136.0.4 and Firefox ESR versions 115.21.1 and 128.8.1. The vulnerability is similar to a recent zero-day exploit in Google Chrome, CVE-2025-2783, which was used in cyber-espionage campaigns against Russian entities. Additionally, Mozilla previously addressed another zero-day vulnerability, CVE-2024-9680, exploited by the RomCom cybercrime group, allowing code execution within Firefox's sandbox. Earlier in the year, Mozilla responded to two zero-day vulnerabilities exploited during the Pwn2Own Vancouver 2024 hacking competition.