Multiple flaws were found in the processing of malformed web content. A web page containing malicious content could cause Firefox to crash or, potentially, execute arbitrary code with the privileges of the user running Firefox (CVE-2018-5089, CVE-2018-5091, CVE-2018-5095, CVE-2018-5096, CVE-2018-5097, CVE-2018-5098, CVE-2018-5099, CVE-2018-5102, CVE-2018-5103, CVE-2018-5104, CVE-2018-5117).
To mitigate timing-based side-channel attacks similar to "Spectre" and "Meltdown", the resolution of performance.now() has been reduced from 5μs to 20μs.