Tab sidebar extension which you can preview and manage multiple tabs in Firefox,provides a sidebar in the browser that can act as a replacement to the main tab bar, complete with always visible preview thumbnails and in tab navigation buttons.
To enable this extension in your firefox,first make sure you have firefox 3.5 updated.
Go to this page and install the extension.

After installed tab sidebar,go to Tools->Add-ons.Click on Preferences,and you can select sidebar position in your firefox window.


Now,enable tab sidebar from View->Sidebar->TabSidebar


Since Tab Sidebar provides a replacement for the main tab bar, when the sidebar is visible Firefox’s main tab bar will be hidden. If you still wish to use the main tab bar then you can show it again from the Tab Sidebar options.