According to the release notes, Firefox 57.0.2 fixes two bugs, neither of which is related to security. And yet there’s also a security advisory for Firefox 57.0.2, which lists two vulnerabilities fixed in the new version.
In the past, Mozilla linked to relevant security advisories on Firefox release notes pages, so presumably someone simply forgot. Fixes for security bugs are a lot more important than fixes for obscure non-security-related bugs, so hopefully this isn’t the new normal for Firefox release notes.
Since this update includes security fixes, it’s a good idea to make sure your Firefox installation is up to date. You can do that by clicking its menu button at the top right (three horizontal lines, sometimes referred to as a ‘hamburger’ button), then choosing Help
> About
.