When I use the search box to enter a keyword, this keyword is always displayed in the search box whether the search is complete or not. I think the search box retains the input keywords is for the user switching between different pages to find the content to be searched. But for the content that has already been searched, it is not necessary to retain the keyword. When users search for new content, they need to delete the original input which makes them add a step. On the other hand, it is easy to inadvertently reveal some privacy if search content be retained. So I think we can add a judgment on whether the input content has been searched. If it is done, then empty the search box. Or add a setting for this operation, the user can arrange for themselves

For me, this is actually quite useful functionality, that I've used a lot. Sometimes I'll have done a search on my default engine, then wanted the same term on a different engine - I can just go back to the search bar, click, and click the different engine. I can also alter my term at the same time. Note that on Windows & Mac the search box is select all on click, so you can just start typing and it'll erase your existing text. On Linux, it is different due to how paste (and especially middle-click paste) works.

Oh, I just realised this is a dupe of bug 253331.