Turn off autocomplete on the query field.

Long autocomplete menus drop down and obscure the top of the as-you-type search results, which are what the user is looking at to see whether he's found what he's looking for.
Give the case-sensitivity checkbox an accesskey.

In Firefox 29 on the Mac, control-option-C does check and uncheck the checkbox, as long as the search field isn't focused (which is an unfortunate caveat).