If like me you work with browsers and web pages on a daily basis then you might find this extension to Mozilla's Firefox a useful tool.
The extension simply adds a web developer toolbar to Firefox enabling you to perform many annoyingly awkward functions of web development much more efficiently.
One of my favourite features enables you to edit a sites' stylesheet on-the-fly. Other features are very useful too, such as the handy view source button, the browser resolution resize button and cookie information retrieval.
It also enables you to validate a page and outline various page elements including depreciated elements etc.
This toolbar is a must for any Web Developer.