Google has been working on its Manifest v3 for Chrome Extensions since late last year. An early draft of v3 has developers and other browser makers asking questions and scrambling for answers. Because Mozilla's Firefox WebExtensions API is compatible with Manifest v2, developers have many questions for how Mozilla will respond to Manifest v3. Mozilla addressed some FAQs in a recent blog post.
One of the v3 updates is the deprecation of the blockingwebRequest API. The API gives extensions the ability to intercept inbound and outbound traffic and then block, redirect or modify as needed. Google is replacing it with the declarativeNetRequest API. The new API limits the number of rules available when blocking content as well as filters and actions. Mozilla has pointed out that certain browser developers will need to use additional functionality beyond declarativeNetRequest to keep the same level of control in a v3 environment.
While Mozilla is independent of Google and offers its own competitive browser (Firefox), the company has indicated the importance of maintaining compatibility. After all, there is no single standard for browser extensions. But, Mozilla has indicated it has "no immediate plans to remove blockwebRequest." Mozilla is currently evaluating other v3 features including background service workers, and runtime host permissions.
Some v3 features and functionality will remain the same such as cross-origin communication. However, v3 is not backward compatible. While v3 remains in draft stages, Mozilla will continue to monitor development and update its developer community regarding changes, issues, and implementation strategies.