Took me a couple of seconds to figure this one out- after upgrading to latest version of Firefox the fist thing I noticed was I no longer had a back button for my browser. I use this HEAVILY and can’t believe I am the only one. Not sure why they would remove this function from the navigation toolbar. As is you can go back in FireFox by right clicking mouse and clicking back or do same by clicking Edit menu. What a drag!
Restoring you back button in Firefox is relatively easy and takes about 5 seconds. Go to View->Toolbars-Customize. You will see set of arrows ( back/forward) drag this button to your navigation toolbar and voila!