• Reported by Nate

The pnhtoolbar is a Mozilla add-on which provides a nice collection of features for web developers. The features are based off of ideas from existing bookmarklets.
Currently active features include (from the pnhtoolbar page):

• Links to most W3C Specifications
• Automated submission to many validation tools
• Hide & show style sheets
• Apply your own external style sheet
• Highlight many HTML elements
• Resize Window to specific dimensions for testing
• Highlight form information
• View page cookies

There isn't a Firebird (Phoenix) version, but it seems to be a handy thing to have installed on your various mozilla based browsers. I've got it working here on the Win2k and OSX versions of Mozilla.
Via blogzilla.