Originally Posted by felgall
Internet Explorer and Chrome - press F12.
Opera - press CTRL-Shift-I.
Firefox is the only popular browser that doesn't have proper developer tools built in and relies on extensions instead to add the functionality provided native in other browsers.
Well, sorry about that, it's nice to know about, I have used that feature before but did not know it could do all those things, and I still like the Firefox way because I can see the entire page source in fullscreen. And thank you for that information.