For those of you blithely surfing the web in total ignorance like myself, it seems that the newest version of Pale Moon will no longer tolerate Ad Block Plus. I was a bit surprised to see a pop up that told me the add-on was disabled, and there was no way to turn it back on.
Never fear, there is a direct substitute designed for Pale Moon called Ad Block Latitude. It uses the same filter list I had in Ad Block Plus.
It seems to have the same functionality, with the exception that I couldn't see a control to allow certain ads. Not that many of us would use it.