There are a few tools that I find very useful when working on websites. Recently I've had several people asking me about them and it seems that they are quite useful even if you're just viewing a site, so I though I would share them here...

These are all Firefox add-ons, so if you are a die-hard Internet Explorer user, you'll need to install Firefox to use these tools.

1. Firebug - I use this tool more than any other, hands down. This tool allows you to see what is going on behind the scenes of a website.
   https://addons.mozilla.org/en-US/firefox/addon/1843
2. Page Speed - Published by Google, this Firebug add-on helps optimize a webpage for speed. http://code.google.com/speed/page-speed/
3. PDFIt - As thee name implies, this cool Firefox add-on lets you save a webpage in PDF format It is awesome for creating a portfolio, sending a shot of a website to someone or otherwise creating a static document of a website.
   https://addons.mozilla.org/en-US/firefox/addon/7528
4. ScreenGrab - This is probably the second most-used add-on that I use. This allows you to save the webpage to either jpg or png, or copy it to the clipboard. It allows you to save either the whole page, visible section or selected area. I use this a lot to copy and paste website screenshots to an email.
   https://addons.mozilla.org/en-US/firefox/addon/1146

If you are looking to work with SEO, another useful add-on is SEO Quake.
https://addons.mozilla.org/en-US/firefox/addon/3036