What is an Extension?
What does Loadkit Integration Module do?
By installing Loadkit Integration Module on your browser, Loadkit automatically catches downloads (shows up when you click a download link for example), so you won't need to type or copy/paste urls from your browser to Loadkit.
The Add-on is already reviewed and signed by Mozilla. If you open the link by Firefox, it will install the Add-on automatically, otherwise, you need to open the downloaded file later with Firefox.