That type of feature is long gone from Firefox, but there are extensions tht restore that setting. This is the most popular extension that I am aware of with a setting like that. https://addons.mozilla.org/en-US/firefox/addon/classicthemerestorer/

Try the userChrome.css solution I posted in this thread:

• [/questions/1049464] Bookmarks toolbar POSITION resets to the very top after closing firefox

Add code to the userChrome.css file below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

#navigator-toolbox toolbar:not(#nav-bar):not(#toolbar-menubar) { -moz-box-ordinal-group:10; }
#TabsToolbar {-moz-box-ordinal-group:1000!important;}

The customization files userChrome.css (user interface) and userContent.css (websites) are located in the chrome folder in the Firefox profile folder.

• http://kb.mozillazine.org/Editing_configuration