Browser Web Development Tools

Internet Explorer 8 (ie8):
F12 -or- Alt > Tools > Developer Tools

Safari:
Alt >Edit > Preferences... > Advanced > Show Develop menu in menu bar.
Ctrl+Alt+I -or- Alt > Develop > Show Web Inspector.

Firefox:
Install Firebug (http://getfirebug.com/)
F12 -or- Alt > Tools > Firebug > Open Firebug