I'm in the Mojave beta program, currently on Mojave 10.14.1 Beta 4 with Safari 12.0.1.
I noticed that ABP was no longer showing an icon in the Safari toolbar, so I right-clicked and chose Customize Toolbar... to see if I could put it back. But ABP is not shown as one of the icons available for use.
I then went to Safari -> Preferences -> Extensions. Both AdBlock Plus and AdBlock Plus Icon were listed and enabled. The installed version was listed as 2.0.1. I noticed on adblockplus.org that the current version was 2.0.3, so I dragged AdBlock Plus.app from the Applications folder to the Trash and then emptied the trash. This caused both ABP extensions to disappear from the Safari -> Preferences -> Extensions window.
I then installed AdBlock Plus from the Mac App Store, verifying that its version number was 2.0.3. This caused AdBlock Plus and AdBlockPlus Icon to reappear in Safari -> Preferences -> Extensions, but there, the version number was still listed as 2.0.1. The behavior is still as before - no icon. ABP does seem to be working and becomes disabled for a page when the Safari Enable Content Blockers checkbox is unchecked.
Is AdBlockPlus Icon entirely vestigial now? Why does it still install?