The Firefox 1.x classic default themes, called Pinstripe on Mac and Winstripe on Windows, are available for your installing and downloading pleasure.
These are simply stand-alone versions of the Firefox themes before the Firefox “visual refresh” landed. The themes require at least Firefox 2.0b1. I will work on them in the coming weeks to smooth out the rough spots. I tested the themes on my machines but they may be buggy. Please let me know if they don’t work for you.
By the way, you can get the Illustrator and Photoshop files used to make these themes here.