Security update for MozillaThunderbird (important)

This update for MozillaThunderbird to version 52.3 fixes security issues and bugs. The following vulnerabilities were fixed: - CVE-2017-7798: XUL injection in the style editor in devtools - CVE-2017-7800: Use-after-free in WebSockets during disconnection - CVE-2017-7801: Use-after-free with marqu...