End of an era for ad blockers in Google Chrome
Google recently released Chrome 149, which will be the last version of the popular web browser to support an important feature widely used by ad blocker extensions.
From Chrome 150, the browser will no longer allow the installation of extensions that rely on Manifest V2 (MV2), a standard that governed browser extensions for over a decade.
MV2 is being replaced by Manifest V3 (MV3), which specifically dropped support for a feature called Blocking WebRequest, with Google citing privacy, security, and performance considerations.
The final removal of MV2 support from Chrome was flagged by Anton Bershanskiy, a software engineer and open-source developer involved in web standards.
Raymond Hill, the creator of uBlock Origin, explained that MV3 did not make it impossible to offer ad blocker extensions in Chrome, but severely inhibited their ability to do certain advanced filtering.
Chrome’s transition from MV2 to MV3 also wasn’t a sudden, unexpected change. Google has been talking about Manifest V3 since October 2018.
To prepare for the shift, Hill developed uBlock Origin Lite, a version of his popular extension designed to be entirely MV3-compliant.
Because the change from MV2 to MV3 is so dramatic, Hill said he would not automatically transition uBlock Origin users to uBlock Origin Lite in the Chrome Web Store.
“I consider uBO Lite to be too different from uBO to be an automatic replacement,” he said.
“You will have to explicitly find a replacement to uBO according to what you expect from a content blocker. uBO Lite may or may not fulfil your expectations.”
Other popular ad-blocking extensions have adapted to the new standard, but Hill explained that this required making significant trade-offs.
He said the trickery other content blockers use to try and keep their level of filtering the same between MV2 and MV3 meant they risk being less reliable.
Hill published a video showing that AdBlock Plus did not always block ads immediately after Chrome started up. uBlock Origin did, but at the cost of many filtering capabilities.
The Manifest V3 era
When Google announced more details about its plans for MV3 in 2019, it said there had been a lot of confusion and misconception around the motivations and implications of the change.
“This included speculation that these changes were designed to prevent or weaken ad blockers. This is absolutely not the goal,” Google stated.
“In fact, this change is meant to give developers a way to create safer and more performant ad blockers.”
In comments included with the source code commits that removed support for Manifest V2 extensions from future versions of Chrome, the developers explained the reason for the change.
“MV2 extensions are no longer allowed in any supported version of Chrome, and we are removing support for them and the associated functionality,” said Devlin Cronin, extensions platform technical lead.
“We won’t be able to provide or maintain this functionality indefinitely due to the complexity and tech debt, as well as the security risks it entails.”
Cronin said they had found a number of bugs that were specific to MV2 recently. He also noted that other browsers could continue supporting the standard if they wanted to.
“I can certainly understand the desire to keep using these extensions, and if I recall correctly, many of the Chromium forks plan to continue supporting MV2 indefinitely.”
Among Chromium-based browsers, Brave, Opera, and Vivaldi have pointed their users towards their built-in content filters, which are not impacted by changes to the web extension API.
Microsoft Edge is expected to follow Chrome’s lead and completely remove the flags controlling MV2 availability, permanently disabling older extensions.
Firefox, which is not based on Chromium, said it would continue to support Blocking WebRequest while offering both MV2 and MV3 for extension developers.
“More tools for developers means more choice and innovation for users,” said Mozilla, the organisation behind Firefox.
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