This is and great tool bar for your web browsers, you can even resize the view for mobile up to PC sizes to check responsive suites and themes.
(http://smf.surfacethemes.com/index.php?action=dlattach;topic=277.0;attach=43;image)
Get it for your browser :
http://chrispederick.com/work/web-developer/ (http://chrispederick.com/work/web-developer/)
maxx