This is true for all versions of Firefox, and so's the solution: go to Tools/ Options/ Advanced/ General, and uncheck "Start to search when I start typing."
The trade-off is that you'll have to type (modifier)-F to "Find," but you'll be able to do what you really NEED to be able to do on the net, which is quote previous Cow posts in your own new post. :-)
Thanks for wanting to do this!
Tim
Tim Wilson
Associate Director, CreativeCow.net
Associate Publisher,
Creative Cow Magazine!