Blockable items list has been replaced by a Developer Tools panel - press Ctrl+Shift+I (Cmd+Option+I on macOS) to open Developer Tools, then switch to the Adblock Plus panel. A move obvious way to open it would be great but sadly currently not possible (we filed a Firefox bug on that a year ago). You might need to reload the page, requests performed before the panel was opened aren't being displayed. As to Element Hiding Helper, it's sadly not possible to make it compatible with Firefox 57 but we want to incorporate parts of its functionality in Adblock Plus later.