Hi,
There's a hidden config window in FireFox where you can 'fix; this.
1) In your address bar, type 'about:config' without the quotes, and hit enter.
2) You'll get a humorous about voiding your warranty (what warranty?!). Dismiss this and continue.
3) You'll then see a huge list of settings, this is effectively looking under the hood of your browser.
4) in the search box at the top of the window, type drawInTitlebar.
5) You'll see a single setting returned called 'browser.tabs.drawInTitlebar'.
6) Double click anywhere on this line to toggle between true and false.