After I found the icon (look in the address bar when you're on your HumbleBundle.com account-page), this extension worked a treat.
Just open up a humblebundle collection on your account, then click the icon, select the formats you wish to download, and it'll download the files at the same time, sorted in nice folders for each collection.
A feature I included is on a click on the icon (that appears only on humblebundle website), you'll be redirected on the collection page (if you are not already on a download page).
