In 2015, Mozilla adapted the Firefox browser for Windows 10, which among other things offers an integrated Internet search. The search engine used by this feature cannot be selected directly from the Windows settings. Mozilla has been criticized for changing this search engine when Firefox is used as the default browser and its own default search engine differs from Windows' preferred (and unchangeable) Bing search. The user cannot accept or decline this change, he will not even be notified of this change.[112]

In 2014, Mozilla was criticized for integrating support for Encrypted Media Extensions, a copy protection for multimedia, into Firefox for Windows. Mozilla argued that this copy protection is used in many large streaming media services and that it is necessary to support it so that Firefox does not fall behind other web browsers where this support is already fully implemented. Critics pointed out that the implementation of copy protection uses source code that is not open source. This violates the principles of open source software.[113]

The Mozilla Foundation has also been criticized for jeopardizing or abandoning its past ideals in exchange for large financial contributions from Google.[114] (See also Financing and Advertising)

Older versions of Mozilla Firefox have been criticized for using too much system resources.[115] The developers stated that this behavior was partly intended, so from version 1.5 more open pages would be cached for faster navigation if there were enough resources available on the system.[116] However, this improved with newer versions of the browser.[115] Version 3.0 was successfully optimized to reduce resource consumption, among other things.[117][118][119][120]

At the end of 2017, users criticized the bundling with the Cliqz add-on, which was initially supplied as a test with one percent of Firefox downloads from Germany and activated by default. Possible data protection restrictions were criticised, as user input was sent to the servers of Cliqz GmbH, a company mainly owned by Hubert Burda Media, in order to display surf suggestions when typing in the address bar.[121][122]

In December 2017, the unsolicited installation of an add-on for US Firefox users to promote a US television series that had been broadcast since 2015 caused criticism from users and prominent employees. This add-on had irritated some users because they thought it was a component secretly installed by malware. The critics saw this behavior as contradictory to the goals of the Mozilla Foundation.[123][124] Mozilla apologized and withdrew the automated installation of the add-on[125] and, after an internal investigation a month later, announced changes to the so-called "shield studies" over which the add-on was installed.[126]

https://de.wikipedia.org/wiki/Mozilla_Firefox#Kritik