This update for MozillaFirefox ESR 52.5 fixes the following issues: Security issues fixed: - CVE-2017-7826: Memory safety bugs fixed . - CVE-2017-7828: Use-after-free of PressShell while restyling layout . - CVE-2017-7830: Cross-origin URL information leak through Resource Timing API . Mozilla Foundation Security Advisory : - https://www.mozilla.org/en-US/security/advisories/mfsa2017-25/