Several security issues have been found in the Mozilla Firefox web browser: Multiple memory safety errors and use-after-frees may lead to the execution of arbitrary code or denial of service. Debian follows the extended support releases of Firefox. Support for the 52.x series has ended, so starting with this update we"re now following the 60.x releases. Between 52.x and 60.x, Firefox has undergone significant internal updates, which makes it incompatible with a number of extensions. For more information please refer to https://www.mozilla.org/en-US/firefox/60.0esr/releasenotes/ In addition, the new Firefox packages require Rust to build. A compatible Rust toolchain has been backported to Debian stretch, but is not available for all architectures which previously supported the purely C++-based Firefox packages. Thus, the new Firefox packages don"t support the armel, armhf, mips, mips64el and mipsel architectures at this point.