The search engine is the main part of any browser. All browsers have a default search engine, such as Chrome with Google, both of which are owned by the same company, or Mozilla Firefox, which uses an external search engine. In the case of Firefox, it uses Google by default, but Mozilla is already considering Bing as an alternative.
If you are using Firefox and your default search engine has changed, you may have been selected for the most recent Mozilla search engine search. From time to time, Mozilla conducts studies to collect data to improve the user experience. The last thing we learned about it was to change the browser's default search engine from Google to Bing.
So far, this change has largely gone unnoticed, possibly because it affected less than one percent of Firefox desktop users. The study is expected to run throughout 2022 and allow Mozilla to "better understand the criteria for how desktop computer usage changes when the default search engine is changed."