Simple. Firefox button --> Options --> Uncheck Tabs on Top
In the past I had been able to move, as I wanted, (with some simple procedure) the location of Tabs bar below the bookmarks bar in Firefox.
After re-installment of Firefox yesterday, the Tabs bar of course moved back up above the address bar as the recent versions of Firefox do.
Having forgotten the procedure for moving the Tabs bar down, I looked up Internet for the solution. I could not find a link to a web site which describes the simple procedure.
So I shall appreciate help regarding the above matter.