The Download Now link will prompt a local download of the Firefox extension. To install the extension directly, open the file using your Firefox browser.
From Visibotech:
TooManyTabs is an extension for Firefox. It allows you to store as many tabs as you like by adding extra rows in the Firefox. It saves your browser's space and memory as idle tabs are put aside. The extra rows also help to better prioritize and visualize your tabs.
