Firefox 3.6 was released at the end of last month, bringing with it speed and RAM usage improvements and the new TraceMonkey JavaScript engine. However, it also brought a small UI change that some people may not like. When opening opening a link in a new tab, Firefox now uses the Chrome/IE school of thought, inserting the tab beside the one you are currently viewing. The old behavior was for the tab to open on the far right of the stack.
Want the old tab behavior back? There’s a simple about:config fix.
Open a new tab (:P) and type about:config
into the address bar. You should end up in the configuration key editor. Paste browser.tabs.insertRelatedAfterCurrent
into the “Filter” field. This should narrow down the listing to a single item. Simply double-click the row to toggle the setting from “true” to “false.” You can then close the tab and go back to your browsing.