I have Mozilla/5.0 (X11; U; Linux i686; en-US; rv:22.214.171.124) Gecko/2009032713 Fedora/3.0.8-1.fc10 Firefox/3.0.8 on Fedora 10. My Back button was not highlighted, when browsing. I just went to Address Bar > typed about:config> searched for "back" in the filter field. Found the string browser.backspace_action. Double clicked on it. The default value was set to 2. I made it to 0. Back/Forward button seems working now.