In the "this makes me happy" department, Miles Raymond posted his Power Macintosh 9500 (with a 700MHz G4 and 1.5GB of RAM) running TenFourFox in Tiger. I'm pretty sure there is no older system that can boot and run 10.4, but I'd be delighted to see if anyone can beat this. FWIW, the 9500 was released May 1995, making it 20 years old this year and our very own "Twentieth Anniversary" Macintosh.

And Mozilla says you need an Intel Mac to run Firefox! Oh, those kidders! They're a laugh a minute!

http://tenfourfox.blogspot.com/2015/02/the-oldest-computer-running-tenfourfox.html