Vienna-based advocacy group NOYB on Wednesday said it has filed a complaint with the Austrian data protection authority against Mozilla accusing the Firefox browser maker of tracking user behaviour on websites without consent.

NOYB (None Of Your Business), a digital rights group founded by privacy activist Max Schrems, said Mozilla has enabled a so-called privacy preserving attribution (PPA) feature that turned the browser into a tracking tool for websites without directly telling its users.

“Mozilla's limited test of PPA is a part of our effort to improve invasive advertising practices by providing technical alternatives,” a spokesperson told Reuters. “These techniques prevent any party, including Mozilla, from identifying individuals or their browsing activity.”

While this may be less invasive than unlimited tracking, it still interferes with user rights under the EU’s privacy laws, NOYB said, adding that Firefox has turned on the feature by default.

“It’s a shame that an organisation like Mozilla believes that users are too dumb to say yes or no,” said Felix Mikolasch, data protection lawyer at NOYB. “Users should be able to make a choice and the feature should have been turned off by default.”

Open-source Firefox was once a top browser choice among users due to its privacy features but now lags market leader Google’s Chrome, Apple’s Safari and Microsoft’s Edge with a low single-digit market share.

NOYB wants Mozilla to inform users about its data processing activities, switch to an opt-in system and delete all unlawfully processed data of millions of affected users.

NOYB, which in June filed a complaint against Alphabet for allegedly tracking users of its Chrome browser, has also filed hundreds of complaints against big tech companies, some leading to big fines.