Why Chinese Users Can’t Install Popular Firefox Ad‑Blocker Extensions

Recently a user reported on the official Mozilla forum that Chinese mainland IPs receive a “This page is not available in your region” message when trying to access ad‑blocking extensions such as uBlock Origin, AdGuard AdBlocker, AdBlock for Firefox and AdNauseam on the Firefox Add‑ons store.

Our own tests confirm that the pages for these four extensions display the same notice, preventing installation from the Firefox Add‑ons store.

The server returns HTTP status code 451, which indicates that the content is unavailable for legal reasons.

In 2017‑2018, Beijing Mouzhi Firefox Information Technology Co., Ltd. (Mozilla’s wholly‑owned subsidiary in China) faced lawsuits from several domestic companies over ad‑blocking, and a 2019 judgment remains in effect; it is unclear whether the current block is related to those cases, and Mozilla has not responded publicly.

Only the four extensions mentioned above are affected. Other ad‑blockers such as Adblock Plus and Ghostery continue to work, and all other types of extensions are unaffected and can be installed normally.

Because all Firefox versions share the same addons.mozilla.org domain, both the domestic and international builds of Firefox are impacted.