Mozilla Firefox is a free and open-source web browser that displays online pages using the Gecko rendering engine, which adheres to current and future web standards.
Mozilla disabled malicious Firefox add-ons installed by around 455,000 users, after finding out that they were misusing the proxy API to block Firefox upgrades.
The Bypass and Bypass XM add-ons intercepted and redirected web requests to prevent users from obtaining updates, updating remotely controlled content, or accessing updated blocklists.
To prevent additional users from being impacted by new add-on submissions misusing the proxy API, we paused on approvals for add-ons that used the proxy API until fixes were available for all users.
Starting with Firefox 91.1, Firefox now includes changes to fall back to direct connections when Firefox makes an important request (such as those for updates) via a proxy configuration that fails.
Ensuring these requests are completed successfully helps us deliver the latest important updates and protections to our users.
To prevent other malicious add-ons from abusing the same API, Mozilla has developed a system add-on called Proxy Failover that is hidden, hard to disable, and updates itself indefinitely.
This new add-on protects current and older Firefox