You can do it a little differently than IE, if you really don't like popping up another input (i don't see why this is 'silly', though...) by hitting a key-combo other than Enter after putting terms in the URL bar, which will execute a macro instead of attempting to resolve the terms as a URL... or, you can make a macro that actually inserts the search URL into the URL field, with the caret in place for you to just type your terms after it - i did it that way before the prompt() function was available in macros.
If any of those ideas appeal, but you need more specific examples of how to implement it, i'm sure someone will be willing to help.