For the last eleven years, Firefox Search Engine add-ons have been powered by OpenSearch. With the recent implementation of the search overrides API, a WebExtensions API that offers users more controls for opting into changes, Mozilla intends to deprecate OpenSearch and eventually remove it from Firefox. Search Engine add-ons will be removed from AMO on December 5, 2019.

For Search Engine add-ons to continue working, they must be converted to an extension using the WebExtensions API by December 3, 2019. For more information, please see the following documents on MDN web docs:

Unfortunately, it is not possible to automatically migrate users of Search Engine add-ons to their replacement extensions. If you are the developer of a Search Engine add-on, we recommend linking to your new extension’s listing page from your search add-on’s listing page so your users know where to install the update.

If you have any questions, please ask them in our community forum.

October 21, 2019 update: we have heard several requests to explain the rationale behind deprecating OpenSearch. From a security standpoint, Search Engine add-ons provide an attack vector for malicious actors to compromise user profiles. Because Search Engine add-ons are unsigned, Mozilla has limited ability to discover, block or mitigate malicious actors.

This change will also help unify all Firefox add-ons under the WebExtensions API, making it easier for us to provide good tools and documentation to developers.

We also want to clarify that this announcement and the dates we specified only cover our plan for AMO. As long as Firefox supports OpenSearch, those features in the browser will remain unchanged. More details about support in Firefox will be published in the Future Releases blog.