All this does is send your keywords to a normal Google search with an appended &nfpr=1, which prevents the spellchecker from second-guessing what you really meant to search for. You'll still get the patronising Did you mean message at the top if it thinks it's cleverer than you, but at least you can rely on the search results reflecting what you were actually searching for.
Unfortunately, when you use the search box on the results page, it'll try to be clever again, so better use the back button and use this form again.
In Firefox, type about:config in the URL bar, promise to be careful, then search for the option keyword.URL, double-click it and enter http://www.google.co.uk/search?nfpr=1&q= as its value. Navigate away from the config editor. From now on, whenever you type something in the URL box that isn't a valid URL, you'll be taken to Google's search results without the pesky spellchecker interfering.