Chrome 88 will come with Manifest V3 support for the Declarative Net Request API and other changes proposed as part of it. It clarifies API and feature changes in the Chromium project that also bring a number of restrictions for extensions. The most affected extensions are ad blockers, that will stop working properly. One of them, uBlock Origin, is already known for being incompatible with Manifest V3.
Google noted that they will keep the current Manifect V2 available for some time, and didn't define its removal date yet. Anyway, it is an unpleasant change for those who rely on ad blockers.
Manifest V3 removes the blocking feature of the webRequest API, which is used by ad blockers, including the popular uBlock Origin and Ghostery extensions. According to Google, the feature allowed extensions to obtain sensitive information about what you browse, which they don't want.
Additionally, Manifest V3 denies extensions from running remote code, making extensions easier to audit. While it sounds good, this will break a number of extensions that run "user scripts" to change the appearance and behavior of sites on the user side.
So, after uncertain period of time, this will end up making Chrome more secure, but some of the popular extensions will stop working. What about other browsers?
Firefox is not going to adopt the change for now. There is no plan to implement this restriction in the Firefox browser as of now.
Edge already allows testing the Manifest V3 feature, so it will follow Google with this move.
Vivaldi and Brave, two Chromium based browsers, won't enable Manifest V3 as long as they can. However, I doubt that this will last for long. It will require extra cost for them to keep the Chromium code base unlinked from the mainstream.
Chrome 88 will hit the stable branch in January 2021. By that time, Google will accept extensions compatible with Manifest V3 in its Web store.