New version for SeaMonkey on addons.thunderbird.net!
Full list of changes since 1.0:

v2.5 - September 20, 2020
*Major code cleanup.

v2.4 - August 28, 2018
+Added Lithuanian localization.
*Updated French localization. Still need Bulgarian, German, Esperanto, Hungarian, Korean, Macedonian, Turkish, Vietnamese, and simplified Chinese updates.
*Improved namespacing to prevent issues with ES6.
*Fixed automatic adding to the navigation toolbar on fresh install for SeaMonkey.
*Workaround for disabled AutoPlay blocking the audio file playback feature.
#Duplicated Ukrainian localization for uk-UA.

v2.3 - May 10, 2018
+Added audio playback "stop" command while playing alert audio.

v2.2 - May 6, 2018
+Added missing localizations (partial).
/Need help translating new audio file feature for the following languages:
/Bulgarian, German, Esperanto, French, Hungarian, Korean, Macedonian, Turkish, Vietnamese and simplified Chinese

v2.1 - March 27, 2018
*Corrected icon paradigm.

v1.1 - October 25, 2017
#Changed update system to use my own website instead of relying on AMO.
#Changed preference save location.
+Added audio file playback feature.
*Fixed SeaMonkey support.

Added SeaMonkey support.
Added PaleMoon target application entry.
Added Public Domain notice to source files.
Upped version compatibility numbers.

Just a version compatibility update.

+Updated for Firefox 4.
+Added publish date to version number.
+Added clocales for Bulgarian, Danish, Spanish, French, Hungarian, Korean, Macedonian, Ukrainian, Vietnamese, and Chinese (Traditional).

#Rewrote dialog entirely. Hopefully, it'll work correctly on all Operating Systems.
+Added locales for German, Dutch, Polish, Portugese (Brazilian), Russian, Serbian (Serbia), Turkish, and Chinese (Simplified). Thank you BabelZilla.org.

#Fixed dialog for MacOSX (I hope).
#Changed tooltip style.
+Added 24x24 pixel icon set.
#Changed to a CSS-based icon system.