It seems like you can change your default search engine by scrolling on the search bar (in my experience, this has only worked if I pinch/zoom on the bar). I tend to magnify pages with small text by pinching to zoom on my touchpad. If the cursor happens to be on the search bar, I would accidentally change my search engine and have to go to settings to change it back to my preferred engine. It doesn't seem like I can disable this functionality, hence this feature request/idea.