What about the first two steps in Navigation buttons like back, home, bookmarks and reload are missing? Did you try those? If you've gotten to the point where you need to reset using Diagnose Firefox issues using Troubleshoot Mode, make sure that Firefox is not running, when you start in Safe Mode. To make sure, right-click on the taskbar, and select "Task Manager". Open the Processes tab, and make sure firefox.exe is not running.

* If the menu bar is hidden then press and hold the Alt key down, that should make the Menu bar appear (Firefox 3.6 on Windows) (see Restore the Menu bar in Firefox).
* Make sure that you have the Navigation Toolbar and other toolbars visible:  View > Toolbars .
* If items are missing then see if you can find them in the  View > Toolbars > Customize  window.
* If you see the item in the Customize window then drag it back from the Customize window to the Navigation toolbar.
* If you do not see that item then click the  Restore Default Set  button in the View > Toolbars > Customize window.

See also Back and forward or other toolbar buttons are missing and Customize Firefox controls, buttons and toolbars See http://kb.mozillazine.org/Toolbar_customization ..........

* If the above steps didn't help then see http://kb.mozillazine.org/Corrupt_localstore.rdf
 Note: Do not delete localstore.rdf in the program folder (Windows: "C:\Program Files\Mozilla Firefox\defaults\profile\") (Mac: "/Applications/Firefox.app/defaults/profile/")