When testing your web pages, there’s nothing better than testing them live. To do this, you need a web browser and you’ll be able to see the pages as the millions of other (potential) users will browse your site, worldwide.
However, your pages do not need to be online to view them in a browser. You can access the pages from a localhost or across the network. If you have a fast broadband connection, you can test them on a pre-live server which your developers may use for testing pages before they commit changes.
Firebug is a Firefox extension that you can use to edit, examine and test your pages, either locally or live.
With Firebug, you can quickly examine, check and even edit code from the web page. If you think the style sheet applied to the page needs some work, then you can use Firebug to make changes to the CSS and see how it affects the page, before you commit the change. The extension will also enable to check your page load, to see what elements affect the loading time of your site.
This is a potentially interesting extension for developers and users who have to test the code before they allow a site or page to go live.