Firebug Extension


#1

https://addons.mozilla.org/en-US/firefox/addon/firebug/

Firebug integrates with Firefox to put a wealth of development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.


#2

FYI, Mozilla shut down Firebug. It is not longer compatible with Firefox 57