UPDATE: Unfortunately, Google is no longer letting users manually specify that they want all results, making the URL below useless. For those who still want access to a more simplistic interface I suggest using Google mobile located at https://www.google.com/m or an alternate search provider such as Teoma. The plugin listed below however, still works great for adding additional search providers to your Firefox search bar.
Google recently changed the way their search looks to more closely match the enhancements offered by rival search provider Bing, but many users do not like the new interface.
I reported previously during the test period that it was possible to disable the everything sidebar by clearing cookies, but now that the interface has been deployed to the general public this trick no longer works. But do not despair, if you still prefer the old interface there is still an easy solution: simply set your google homepage and bookmarks to http://www.google.com/webhp?hl=all&source=hp.
To fix the search bar in firefox simply install the “add to search bar” add-on, restart firefox, and go to your new google bookmark (http://www.google.com/webhp?hl=all&source=hp). Next right-click on the search input box (where you normally type what you want to search for) and select “add to search bar” and that is it! Enjoy having your old google back!