Mozilla announced that the Firefox browser will fully embrace the next iteration of the Web extension platform, Manifest V3, by the end of 2022, and before then launch a new developer preview program to collect Web developer’s feedback.
Manifest V3 is the latest change to the web extension platform, designed to make extensions safer, faster, and more privacy-friendly. First released by Google in 2019, it can be said to have caused quite a bit of controversy.
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One of the most controversial changes in Manifest V3 is the removal of the Web Request API in favor of the new Declarative Net Request API. The change was heavily criticized by developers as it stripped many extensions of functionality and reduced efficiency. Google Chrome has stopped accepting new extensions based on Manifest V2, and existing Manifest V2 extensions will be discontinued after January 2023.
Mozilla said they were aware of some controversial content in Manifest V3, and for this reason, Mozilla will take a different approach than Google Chrome in implementing Manifest V3. Mozilla believes that the new Declarative Web Request API is not a perfect replacement for the Web Request API, which limits the use of ad blockers and privacy extensions. Therefore, Firefox will retain support for “Block Web Request” in Manifest V3, while also supporting declarative web requests.
Also, Mozilla doesn’t like the Background Service Workers used by Chrome because it doesn’t support many use cases and requires developers to rewrite most of their extension code.
Mozilla proposed Event Pages last year to address these issues and said it has been well received by the community and will be fully supported in Firefox’s Manifest V3. Mozilla says it will also support Service Workers for compatibility reasons.