If this is something that you really want, why not pick it up yourself? Based on your XP, I'm assuming that you have reasonable programming skills. All you really need is a knowledge of JavaScript and XUL. You already have a working application to play with, so it's not like having to start from scratch.
If you are not familiar with JavaScript, there are a billion and one resources out there to help you. If you are not familiar with XUL (more likely), here is a tutorial (developer.mozilla.org) and there is also xulplanet.com, although the latter site doesn't appear to be working as I write this.
I have written a couple of FireFox extensions to complement Perl web applications that I have written. It's not as hard as it might seem - packaging is far more fiddly than writing the actual code, or at least that has been my experience. I certainly think that it's a skill worth acquiring for any developer that is also a FireFox fan. (If nothing else, you can combine the functionality of various toolbars and get some of your screen back!)