DownThemAll! is a download manager/accelerator built as an Addon in Mozilla Firefox. Currenty, DownThemAll! is not compatible with Firefox Quantum.

You will get the following message when visiting DownThemAll! webpage:

This add-on is not compatible with your version of Firefox.

One alternative for DownThemAll! is uGet. uGet is an Open Source and multi-platform download manager. It works in Linux, BSD, Android and Windows.

uGet is a stand-alone application but you can install a Firefox Addon to replace Firefox’s default download manager.

Install uGet in Ubuntu

sudo add-apt-repository ppa:plushuang-tw/uget-stable
sudo apt update
sudo apt install uget

Install the uget-chrome-wrapper

sudo add-apt-repository ppa:slgobinath/uget-chrome-wrapper
sudo apt update
sudo apt install uget-chrome-wrappe

If uget-chrome-wrapper is not installed properly, you will get this error message:

unable to connect to the uget chrome wrapper

Install uGet Integration Firefox Addon

Go to uGet Integration Firefox Addon page and click “Add to Firefox”