Manifest V3 changes were announced in October 2018. It was meant for the WebExtensions API, Chromium open-source browser engine. Google said that the updates are meant for improving the extension security, assuring greater control to users over the extension activity and site interaction, and better performance from the extensions.
However, extension developers pointed out that the Manifest V3 updates contained changes that crippled the features of parental control enforcement, privacy-boosting extensions, and ad-blockers. Following the backlash, Microsoft backtracked some changes in March and June 2019. The changes being launched for Edge are in the stable and beta releases and will not cripple the ad blockers.