Popular Firefox add-on download manager DownThemAll, following not being updated to support Firefox version 57 Quantum, is now discontinued entirely.
The website going down, alongside the last update to DownThemAll's GitHub repository being over a year ago, shows that the open-source Firefox extension is no longer in development. In addition, the extension no longer works as of version 28 of the Pale Moon web browser that supports pre-Quantum Firefox extensions.
In light of this discontinuation, some of the most popular alternatives found on AlternativeTo include JDownloader and Free Download Manager. Though these are dedicated applications and not browser extensions, some newer and more obscure browser extensions, such as Multithreaded Download Manager, do exist.
As of this post, no one involved with the development of DownThemAll has commented on the website's expiration or the project's halted development.