firefox 58 does not have new addons to customize tab position below address bar, this simple userChrome.css file can be created to achieve it.
1.change to the firefox profile directory this can be found from firefox >> help >>troubleshoot information
#cd /home/pawan/.mozilla/firefox/bl6ofr4t.carmatec/chrome
here create a directory chrome and file userChrome.css then add below lines , restart firefox you should have tabs below address bar now.
#vi userChrome.css
userChrome.css
/* Tab bar below Navigation & Bookmarks Toolbars
For best results, show Title Bar or Menu Bar */
#nav-bar { /* main toolbar */
-moz-box-ordinal-group: 1 !important;
border-top-width: 0 !important;
}
#PersonalToolbar { /* bookmarks toolbar */
-moz-box-ordinal-group: 2 !important;
}
#TabsToolbar { /* tab bar */
-moz-box-ordinal-group: 3 !important;
}
Increasing number of top sites on firefox.
change value of browser.newtabpage.activity-stream.topSitesCount from 8 to 36
