VDH used to work fine, but now it just says "Companion App not installed". So I downloaded the .deb file (I'm on Ubuntu) and installed it. It puts the binary in /opt/net.downloadhelper.coapp/. But still it says "Companion App not installed". So how does it find the binary? It's supposed to look for a .json file, which the .deb file installs in /usr/lib/mozilla/native-messaging-hosts. But wait, Firefox is a 64-bit program, not a 32-bit one (we're in the 21-century now!) so it should be in /usr/lib64, not /usr/lib. So I make a symlink from the lib dir to the lib64 dir. Still doesn't work: "Companion App not installed." :-( I'm giving up since it's already taken a lot of time to discover these bugs. I suspect that it's a minor configuration problem that failed QC. It's probably simple, but it's enough to keep VDH from working at all.