I learned that due to changes in Firefox-based add-ons, PaleMoon 27 was no longer finding any updates for uBlock Origin. However. there is now an add-on available for PaleMoon, called uBlock Origin Updater. Once installed, it will allow PaleMoon to find the latest stable update for uBlock Origin.

It is available here: Pale Moon - Add-ons - uBlock Origin Updater

Also of interest are a number of other extensions for Pale Moon by the developer JustOff. See JustOff's JustOff's Extensions for Pale Moon, Firefox & SeaMonkey as well as Topic: pale-moon * GitHub including a number of themes and other add-ons that were created before the "WebExtensions apocalypse" (his words not mine :) )