What is manifest v3?
Manifest V3 is the upcoming version of the manifest file format used by Google Chrome extensions. The manifest file is a JSON file that contains information about the extension, such as its name, version, permissions, and background scripts.

Manifest V3 includes changes to the extension architecture and API that aim to improve extension security, privacy, and performance. Some of the changes include limiting the access of extensions to sensitive user data, such as browsing history, and introducing new APIs for accessing certain functionalities, such as the network and cookies.

One of the most controversial changes in Manifest V3 is the deprecation of the chrome.runtime.sendMessage() method for communication between content scripts and background scripts. Instead, a new messaging system called message passing with port will be introduced. This has raised concerns among developers who rely on chrome.runtime.sendMessage() for various extension functionalities.

Manifest V3 is currently in development and is expected to be released in the near future. Its release has been delayed several times due to concerns and feedback from developers.
What concerns did the developers have?
Developers had several concerns regarding the changes introduced in Manifest V3, including:

1. Content Blockers: One of the most significant concerns was related to the replacement of the webRequest API with the declarativeNetRequest API. The change limited the blocking capabilities of content blockers, such as ad blockers and privacy-enhancing extensions. Developers argued that the new API would not provide the same level of flexibility and functionality as the old one, which could lead to a decrease in the effectiveness of these extensions.

2. Communication between scripts: As mentioned earlier, the deprecation of the chrome.runtime.sendMessage() method and the introduction of a new messaging system called message passing with port raised concerns among developers who relied on the existing method for communication between content scripts and background scripts in their extensions.

3. Permissions and Privacy: The new permissions system introduced in Manifest V3 aimed to limit the access of extensions to sensitive user data. While this change was intended to improve user privacy, developers were concerned that the new system might be overly restrictive and hinder the functionality of some extensions.

4. Migration effort: Developers expressed concerns about the effort required to update their extensions to meet the new requirements of Manifest V3. Some developers were worried that the changes might lead to significant rewrites of their extensions, which could be time-consuming and resource-intensive.

In response to these concerns, Google has made some adjustments to the proposed changes and has been working with the developer community to address their feedback. The release of Manifest V3 has been delayed to allow for further refinements based on developer input.