Please make sure that you have installed the latest version of IDM (6.38 Build 16 or above).
Please use "Help→Check for updates..." (or "Help→Quick Updates" for old versions) IDM main menu item.
Then please restart your computer. IDM needs to replace all its DLL files for changes to take effect. Without restarting update will not work!
Then please install this extesion: idmmzcc-palemoon.xpi