By Supantha Mukherjee

STOCKHOLM, Sept 25 (Reuters) - 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), the digital rights group

founded by privacy activist Max Schrems, said Mozilla has

enabled a so-called "privacy preserving attribution" feature

that turned the browser into a tracking tool for websites

without directly telling its users.

Mozilla had defended the feature, saying it wanted to help

websites understand how their ads perform without collecting

data about individual people. By offering what it called a

non-invasive alternative to cross-site tracking, it hoped to

significantly reduce collecting individual information.

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 ( AAPL ) Safari and

Microsoft's ( MSFT ) 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, had also filed

hundreds of complaints against big tech companies, some leading

to big fines.