Adds a splash screen when launched. Supports sound, opacity, CSS customization, custom images, and much more. You can add {appVersion}, {buildID} and {userAgent} to the loading text and it will be filled in for you. It is a fork of the discontinued Splash! add-on for Firefox.
Simply download the contents of the "src" folder and pack the contents into a .zip file. Then, rename the file to .xpi and drag into the browser.
Pale Moon Add-ons site or at the repository.