Hi, Joe. Navigational Sounds is no longer available through the AddOn Manager of Firefox. This is because Navigational Sounds no longer works with Firefox Quantum (version 60 and up).

Instead,

1.  open Firefox.

2. Press CONTROL plus SHIFT plus A to open the AddOn Manager.

3. Tab to the list of available categories within the AddOn Manager.

4. The category you want to open is Extensions. When you find it, press ENTER.

5. TAB to the search box and enter

download sound.

6. The AddOn you want to install is:

Download Sound1.4By

BPS

Plays a sound or utters a text using speech synthesis when a download is completed.This simple extension plays a sound or utters a text using speech synthesis

when a download is completed.

This is a deceptive description, because, as installed, it just plays a simple ding sound, once the AddOn is installed.

This is the best way to get a download sound for Firefox downloads.