This is a major development and bugfix release.
DiD This means that the fix is "Defense-in-Depth": It is a fix that does not apply to a (potentially) actively exploitable vulnerability in Pale Moon, but prevents future vulnerabilities caused by the same code, e.g. when surrounding code changes, exposing the problem, or when new attack vectors are discovered.
Update via the internal Updater: Help / About Pale Moon ; or full downloads:
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.]