Due to a conflict with Mozilla, the add-on's developer has taken it off the Firefox Marketplace.
"The uBlock Origin Lite add-on was also accused of collecting user data and running afoul of privacy concerns, which is one of the big reasons why people switch over to the Firefox browser in the first place. Hill [the developer] responded: “It takes only a few seconds for anyone who has even basic understanding of JavaScript to see the raised issues make no sense.”"