That would annoy me too. However, I don't think any changes have been made to default search engine since around December 2014 when the search contract for North America changed. At least not intentionally. I assume you were updating from a much more recent version. Were you able to change your default back to Google and does it stick? Did you notice any other changes? ---- Some users have received a prompt during an update to speed up Firefox by restoring some default settings. If you click that button, the Refresh feature runs and your settings folder is moved to the desktop inside an Old Firefox Data folder. Do you see anything like that?