Quick mode uses 1-9 to toggle visible engines in order. Alt mode uses Alt+1-9. Numpad works too.
Press 0 to clear selected engines. Press it again before changing engines to restore them. In Alt mode, use Alt+0.
Press / or Tab from the homepage to put the cursor in the search bar.
Press Esc while typing to clear the search box and close the suggestion dropdown.
As you type, the dropdown suggests cleaner spelling. Use the arrow to apply it, or copy it without changing your search.