Hey guys! Thanks for this plug-in, finally compatible with Firefox quantum !
For those having troubles with NinjaDownloadManager plug-in configuration, check this out :
You can configure download capture in NinjaDownloaderManager directly (the software, not the plug-in). You have to click on the settings icon (the little gear), then select Monitor and....shazam! you can configure the plug-in download capture and a bunch of other usefull things related to the download capture !!!
Hope it will help !