I looked all over for the Windows theme for Linux, but didn't find what I wanted. However, I found a .jar of the Vista theme, which was good enough for me. I've opened it up, found the blue back/forward button icons, and GIMPed them to orange (to match Human theme). I'm using it now and it looks like just the right thing for bringing a new-OS look to Ubuntu's FF3 while keeping the orange Human theme. Right now it's hacked together (the XP on Vista package was my base, so it still shows up as XP to Vista in the menu) but if I figure out how to fix this I might put it up for download.
Thumbnailed for the fact that 1680x1050 images on forums = bad:
It could've been 3360x1050 if I wanted to...but I turned off my external monitor (1 window expanding across 2 monitors is unusable! especially with the center of the page being where the gap between the monitors is).
If you have any suggestions on other elements to change (mainly color, wanting to keep the Windows-FF3 feel but fit it to the Linux color scheme) then tell me, I just started with this skinning thing but I could probably figure it out.
EDIT:
Got a theme .jar made, tried posting it as an attachment but it's 500kb so wouldn't upload

I would post to my FTP but since we're finishing the basement I took down the server (old Pentium 1 comp) to keep drywall dust out of it. I'll post it to Mozilla's site later. I've tested and it installs fine. I changed a few other UI elements (the close button on tabs, the info button, some arrows) to fit the color scheme better as well.