The deviantAnywhere Firefox extension was one of my favorites for a long while, but it wasn't updated for quite a long time. It's so old that it's still requires the status toolbar to be displayed, even though the thing doesn't exist anymore in the recent versions of Firefox. It was making the notification sounds though.
Using the Firefox Developer Edition 38.0a2 (what would be the alpha channel), which is 64-bit by the way, doesn't even produce any kind of sound anymore. Probably deprecated something that made the extension work until now. That means that when Firefox reach version 38, it will probably stop working altogether for all the other users.
Meanwhile, I noticed that another cool extension I'm using, Video DownloadHelper, was rewroten from the scratch and jumped from their eternal 4.9.something versions to the 5.0 versions. It uses now a new JavaScript-based API which makes it all sort of awesome. Using it makes the extensions restartless, very lightweight and, from what I heard, much easier to maintain.
Since the Chrome extension seems new, I was thinking that maybe you would consider doing a new version for Firefox too.