(Old review Title field that was silently removed per typical Mozilla doctrine of "rip away longstanding useful features Because Modernization":)
== Download done and Download failed no longer work; Options popup has display bugs ==
I have found this add-on essential ever since the Firefox developers ridiculously got rid of the sound you used to get when finding text on a page would wrap back to the beginning (without that, it's easy to waste time looking at the same results in a loop without noticing at first).
I also find the Download done and Download failed sounds very important so I don't have to keep watching the download progress bar during downloads (and don't have to bring up the download popup to explicitly check for failed downloads, since the stupid Firefox UI doesn't seem to let you know about those anymore, at least when saving web pages).
However, unfortunately, the download sounds stopped working at some point. Thankfully, the Findbar wrapped, Session restored, and Popup Blocked sounds are still working (not sure about any others, as those are the 5 I use).
Also, a recently introduced problem is that the Noise options popup no longer displays properly -- the scrollbar is completely off the right side (need to scroll using a mousewheel or trackpad gesture), and the three buttons at the bottom, which are the one for loading and saving settings, and I believe OK and Cancel (not sure since in the developer website screenshots, the last two are labeled in Taiwanese), are almost completely off the bottom of the window, which cannot be resized to make the cut-off controls visible.
I hope the developer gets some time to address these recent bugs soon (the last version came out in 2016-01 as of this writing), so this add-on can return to 5-star territory. I'm not aware of any other add-ons that do the same thing.
== Update, 2018-10-23 ==
At some point the download done & failed sounds started working again (e.g. on Firefox ESR 52.x). I believe what happened is that the events got renamed, as once I got it working, there were two similarly named versions of "done" and two versions of "failed", and only one of each did anything. I think maybe the options popup got fixed too; not sure.
In any case, I thought this was one of the XUL/XPCOM add-ons that would never be ported to WebExtensions, so I'm ecstatic to see that the developer was actually eventuallly able to do it. Unfortunately the options UI for the new one is quite intimidating, requiring events to be added by name with no presets available. It looks like there are now some basic instructions in "About this extension", but I've just been too busy to sit down and figure it all out yet.
I'll update this review (and rating) again once I get the WebExtension version acting like I had the classic one working (or as close to that as the WebExtension API limitations allow you to get). Without a friendlier UI, though, I can't see my rating going above 4 stars.