Mozilla removed it. This can happen when issues are found during the review of the extension or theme, or the extension or theme has been abusing the terms and conditions for addons.mozilla.org. The developer has the opportunity to resolve the issues and make the add-on available again.
Mozilla tekkes-it. Aya yezmer ad d-yeḍru ticki uguren ttwafen deg lqem n uzegrir neɣ n usentel, neɣ ma yella asiɣzef neɣ asentel ur iqudeṛ ara ilugan n addons.mozilla.org. Aneflay ɣur-s tagnit akken ad yefru uguren-a, sakin ad d-yerr azegrir.