Better recommendations: You may see suggestions in regular browsing mode for new and relevant Firefox features, services, and extensions based on how you use the web (for US users only)
Enhanced tab management: You can now select multiple tabs from the tab bar and close, move, bookmark, or pin them quickly and easily
Easier performance management: The new Task Manager page found at about: performance lets you see how much energy each open tab consumes and provides access to close tabs to conserve power
Improved performance for Mac and Linux users, by enabling link time optimization (Clang LTO). (Clang LTO was enabled for Windows users in Firefox 63.)
More seamless sharing on Windows: Windows users can now share web pages using the native sharing experience. You can access Share in the Page Actions menu
Added option to remove add-ons using the context menu on their toolbar buttons
New for enterprise users: Updated the policy engine on macOS to allow using configuration profiles to customize Firefox for enterprise deployments
Various security fixes: https://www.mozilla.org/en-US/security/advisories/mfsa2018-29/
TLS certificates issued by Symantec are no longer trusted by Firefox. Website operators are strongly encouraged to replace any remaining Symantec TLS certificates as soon as possible.
about:crashes has been redesigned to make it clear when a crash is being submitted to Mozilla, as well as being clear that removing crashes locally does not remove them from crash-stats.mozilla.com
The macOS keyboard shortcut to add "www" and ".com" to a URL is now ctrl-enter instead of [apple]-enter
Windows 7 Pro SP1 (64-bit), avast! v17 Free, MBAM3 Pro, Windows Firewall, OpenDNS Family Shield, SpywareBlaster, MVPS HOSTS file, MBAE Premium, MCShield, WinPatrol PLUS, SAS (on-demand scanner), Zemana AntiLogger Free, IE11 & Firefox (both using WOT [IE set to WARN, FF set to BLOCK]), uBlock Origin, CryptoPrevent.
[I believe computer-users who sandbox (Sandboxie) are acting prudently.]