Google has said that it will revise the proposed changes to Chrome's extension API that would have broken or reduced the functionality of a wide range of ad-blocking extensions, to ensure that the current variety of content-blocking extensions is preserved. The initial plans generated a wide backlash from both the developers and users of those extensions, but Google maintains that "It is not, nor has it ever been, our goal to prevent or break content blocking" [emphasis Google's] and says that it will work to update its proposal to address the capability gaps and pain points.
The advertising company is planning an overhaul of its extension interface to, among other things, increase user privacy, make it harder for extensions to perform malicious actions, and make the browser's performance more consistent. Together, this work is documented as Manifest V3.
One of these changes in particular had grave consequences for ad blockers. Currently, ad blockers make extensive use of an API named
webRequest. This API allows extensions to examine every single network request made by a page and either modify it (to, for example, redirect it to a different address or add or remove cookies), block it altogether, or allow it to continue unhindered. This has both a substantial privacy impact (an extension can see and steal your cookies and hence masquerade as you) and, Google said, some performance impact, as every single network request (of which there may be dozens in a single page) has to wait for the extension to perform its analysis.