I'm using Youtube as of 24 Jan 2018, running Tampermonkey 4.5.5660 on Firefox 58.0 on Windows 10 Home Version 1709. The script only works when navigating to Youtube from elsewhere or after refreshing the page. When navigating from within Youtube, the script does not work. It doesn't even show up as enabled on Tampermonkey. This happens with all of the Youtube scripts that I've tried.
Issue with Firefox
I'm using Youtube as of 24 Jan 2018, running Tampermonkey 4.5.5660 on Firefox 58.0 on Windows 10 Home Version 1709. The script only works when navigating to Youtube from elsewhere or after refreshing the page. When navigating from within Youtube, the script does not work. It doesn't even show up as enabled on Tampermonkey. This happens with all of the Youtube scripts that I've tried.