A tip for anyone in my previous situation. You can't change the volume of the sounds but you can add your own sounds. So you can simply add your own, louder sound files, or with some luck find the original sounds this uses (at least some are default Windows sounds stored in C:\Windows\Media) and modify the volume though software or websites.
Personally I found the "Windows Navigation Start.wav" file and modified the volume myself, set it as a custom sound and done.

Great.
It would be nice to be able to configure sounds for additional events. Example:
- tab created
- tab closed
- switch to fullscreen
- exit from fullscreen
- bookmark created / modified
- search engine discovered

This extension is great at what it currently offers, however I have found an issue with the re-triggering navigation start sound.
I hope the developer of this add-on can potentially find a way to tackle this issue.

This extension can in fact be configured. (Thankfully, as I did not like the default complete navigation sound.)

Go to the extension in your list and click the gear to Manage extension.

Then click the 3 dots next to the toggle to enable it and click Options.

Here you can disable any sounds you don't like or upload custom sounds to use in their place. Be sure to click to save your preferences!

Rocking this add-on in Waterfox G5.1.12! 10/10 best extension I ever installed! I'm using it to replace what was the Navigational Sounds add-on I used to use back in the pre-Quantum days.

This addon is one of the most useful I've installed. Firefox's experience is great by itself, but it feels lonely without sounds. This addon gives Firefox that feeling it's missing, and it's great to know what's going on with sound cues. Working great even with a lot of plugins. Thank you Jawhien!

Can I have a sound when I close a tab?(´･ω･`)

Thank you so much God Bless You i been waiting for this so long . I can't believe i missed the old one they use to have for Firefox .

Спасибо за дополнение, очень полезное!
Добавьте пожалуйста, если можете, текстовое уведомление с таймаутом о открытии новой фоновой вкладки.

Navigational SoundsがFirefox Quantumになって非対応の古いアドオンが切り捨てられてから、不便でしたが本当に助かります！ありがとうございます！！！！

Hello,
Is there a possibility of adding options to play feed discovered, serch provider discovered, download failed, download interupted and information/notification bar sounds to the options in the future?
Regards.
Melissa
PS: Doesn't work for all clicking on links some broken as of June 29 2019.

Update (today's date is 1-21-2020): Shortly after I left this review, I switched to Waterfox (which since became Waterfox Classic). Back then, the sounds were working beautifully with Firefox Quantum. I switched back to Firefox just over a week ago (on January 12th) and unfortunately, Mozilla changed something and now Extra Sounds gives me FAR too many Navigation Start clicks, and sometimes they can be too loud. I don't know what Firefox is doing that's so different from a year ago, but good lord. They made Extra Sounds become annoying!!! It breaks my heart. Those bastards. lol Oh well.

Fortunately, I'm actually finding that I'm happier without the sound. Go figure. I guess I've changed! :) Thanks again for your hard work, Jawhien. It's been a damn good run!

Original review below:

This is awesome. I might actually switch to Firefox Qauntum thanks to this (from Firefox 52.3.0 ESR).

I've been using Firefox Quantum as my Amazon Prime Video player ever since Amazon raised their minimum browser requirements (it made me quite angry because I hate Firefox Quantum). My primary browser is Firefox 52.3.0 ESR. One of the many reasons I refuse to switch to Firefox Qauntum has been that I couldn't find a Navigational Sounds equivalent. I've had that feedback sound for as long as I can remember (since Windows 95, I guess, I'm not really sure). So, I kinda depend on it.

Well Jawhien, thanks you to, a major roadblock between me and Firefox Quantum has been removed. There are still a few remaining (I'm finally working on removing them one by one), but this one was probably just about the most difficult one for me to deal with since Quantum's release, and now I no longer have to! I'm very happy. Thank you!

Consider this a very big and warm bro-hug from me to you, man. It's just that big of a deal for me.

Thank you so much !! Basically the same as the old navigational sounds in old firefox.