Open about:config in browser
right clk and choose New, then Boolean
name it browser.tabs.onTop
set to false
if that won't do it, go to the add-ons, look for Tabs On Bottom and accept it.
Long time ago, I had moved my Tabs bar in Firefox to the bottom of all tool bars. Earlier today, it had somehow moved up. So I looked for the boolean key "browser.tabs.onTop" in about:config to move it back to the bottom, but I found that that boolean key no longer exists.
Please help. Thank you!