Nice add-on for Aria2 integration which works perfectly with my configuration: LinuxMint 18.2, Firefox 57. On start up results a blank window but text appears on right click or just enlarging the window's size a little bit from any side you want. Would appreciate the "Open" button to be operationnal (as it's possible with the buit-in Firefox dowloader) as sometimes it's convenient to just have a look at a file and have it simply downloaded in a tmp directory.