Firefox
If you do most of your web development work with Firefox, Firebug has to be one of those extensions you cannot miss, it is like the Swiss knife for this browser; I could describe all their features here but you’d better check it out in their web site:
And here is a screenshot of it working on WordPress admin page:
Firebug on Firefox
Chrome
In the other hand if you use Chrome as your main browser, you don’t need to worry that firebug does not support your favorite browser; Chrome comes with the same set of tools (a handful more features to be honest) out of the box, the good thing about it is that you don’t need to wait for an update when a new version of Firefox breaks the plugin.
Here is a screenshot of it doing its work:
Chrome developer tools
Internet Explorer
Internet Explorer 8 also comes with a set of developer tools but in a less integrated environment (as you can see in the following screenshot):
Internet Explorer developer tools
Anyway if you are used to this browser at least you have some tools to get your work done.
Firebug Lite
Firebug lite is an option that works with all major web browsers, you can check it out in:
http://getfirebug.com/firebuglite
