This article tells how to get Firefox preferences in a pop-up window from Tab one. If you’re used to seeing Firefox options or settings open in a pop-up window, which is going to change with Firefox 38 version (which is now in beta) as Mozilla introduces tab-based preferences or incontent preferences to all users after a long time testing.
Disabling tab-based preferences in Firefox 38
1. Visit about:config from the address bar in Firefox browser
2. Find the preference browser.preferences.inContent and change its value to ‘false’.
3. Now select ‘Options’ in Firefox menu, Settings will open in a window instead in a tab within the browser.