Mozilla expects to launch extensions Manifest V3 support in Firefox in late 2022

Mozilla plans to introduce support for the extensions Manifest V3 in the organization's Firefox web browser in late 2022. Preview versions are already available in development editions of the web browser.

While Mozilla plans to introduce support for Manifest V3 in Firefox, it won't remove support for APIs that are essential to privacy extensions. Content blockers and other privacy extensions will continue to function in Firefox as before, provided that developers continue to support them.

Manifest V3 defines APIs and the capabilities of browser extensions. Google announced the new version of the manifest in early 2019 and revealed that Chrome extensions would have to be updated eventually to remain available for users of the Chrome browser.

The initial version of the draft was discussed controversially. Developers voiced concern over some of the planned changes, as they would limit privacy-focused extensions such as content blockers from working properly. Google made some concessions to developers but continued its work on introducing the new capabilities and removing the old. The company landed Manifest V3 support in Chrome Canary 80 and in Chrome Beta 88.

Firefox extensions won't be limited by Manifest V3

Mozilla announced in 2019 that it would implement support for Manifest V3 in Firefox but would make adjustments to certain limitations. A new blog post on the Mozilla Add-ons Community blog sheds light on the adoption and the differences between Mozilla's and Google's implementation.

The decision to remove the blocking part of the WebRequest API and to replace it with the limiting declarativeNetRequest API was at the center of the controversy. Mozilla notes that the new API limits "capabilities of certain types of privacy extensions without adequate replacement".

Mozilla will keep the WebRequest API in Firefox to make sure that privacy extensions are not limited in providing the functionality they are designed for. The organization will implement the declarativeNetRequest API for compatibility reasons according to the blog post.

Mozilla will "continue to work with content blockers and other key consumers of this API to identify current and future alternatives where appropriate".

Firefox will also support Event Pages in Manifest V3 and introduce support for Service Workers in future releases.

Developer Preview

Developers may turn on the preview in the following way in current development editions of the browser:

1. Load about:config in the web browser's address bar.
2. Confirm that you will be careful.
3. Search for extensions.manifestV3.enabled and set the preference to TRUE with a click on the toggle.
4. Search for xpinstall.signatures.required and set the preference to FALSE.
5. Restart Firefox.

Extensions may then be installed via about:debugging. Permanent installation of Manifest V3 extensions is possible in Nightly and Developer editions of the Firefox web browser. The implementation is not complete at the time of writing.

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Mozilla expects to launch extensions Manifest V3 support in Firefox in late 2022