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Google released a first draft of the new version of Google Chrome's Extension Manifest in January 2019.

The company plans to limit the webRequest API that extensions, content blockers like uBlock Origin or Adblock Plus, use currently to block certain elements on webpages. It would introduce the declarativeNetRequest API instead designed to take over.

The change, if implemented as suggested, would limit content blockers and other extension types significantly in Google Chrome.

Google explained the decision in the following way:

This begins in the browser process, involves a process hop to the extension's renderer process, where the extension then performs arbitrary (and potentially very slow) JavaScript, and returns the result back to the browser process. This can have a significant effect on every single network request, even those that are not modified, redirected, or blocked by the extension (since Chrome needs to dispatch the event to the extension to determine the result).
Basically, Google argues that extensions that use the webRequest may have a significant impact on performance. In other words, using extensions that make use of the API may slow down web browsing measurably.

content blockers performance chrome


Cliqz, a German startup that operates the Cliqz browser and owns the anti-tracking extension Ghostery, ran benchmarks recently to find out whether data would confirm Google's claim.

The company used a large dataset of popular sites and measured the performance of the content blockers uBlock Origin, Adblock Plus, Ghostery, the adblocker of the Brave browser, and DuckDuckGo's adblocker.

One of the core findings of the benchmark was that all content blockers, with the exception of DuckDuckGo's adblocker, added "sub-millisecond median decision time" to each request. In other words, the performance impact of content blockers is negligible.

The test and dataset is available publicly. The selection of content blockers can certainly be criticized, especially since Ghostery is not a full-fledged content blocker like uBlock Origin or Adblock Plus. Gorhill, the developer of uBlock Origin re-ran the test and discovered that Adblock Plus did not perform as well as outlined by the original test results.

Google mentioned content blockers explicitly but other extensions use the webRequest API as well. It is possible that some introduce high cost when using it.

While it is somewhat understandable that Google wants to address performance issues caused by extensions, punishing all for the wrongdoings of some may not be the best course of actions.

To be fair, Google is still discussing changes and noted in a comment that the company does not want extensions to break because of changes made in the new manifest version.


Source: Benchmark refutes Google's claim that content blockers slow down Chrome - gHacks Tech News