How do I disable the "Download completed" sound?

[soundsgoodtome]

Firefox > Add-Ons doesn't display a Preferences button for BMD. So, how do I silence it?

EDIT: Ah. Turns out it was the system-level Notifications feature in the macOS. I keep all notifications disabled, and Firefox isn't my default browser. Apparently BMD is the first Firefox add-on I've installed that decided to send a system-level notification—something I pretty much NEVER hear. So, I thought it was a BMD setting.

I still wish there were a way to disable sound within BMD's notifications. I don't mind seeing a banner, but wish the notification were silent. I know I can disable all sounds in Firefox notifications, but I'd prefer to avoid such a coarse solution—silencing everything. I'd prefer to silence only the apps whose sounds aren't needed.