Did you try downloading it directly from the Mozilla site? (
http://www.mozilla.com/en-US/ (There are links to other languages on the bottom right - yes there is a Dutch version
)
It will download for MacOSX I believe any version X 10.1 up to 10.4 . I've got Firefox on both my G4 and my G5. It shouldn't matter if it is PowerPc or Intel based either because it is based on the operating system.
There are many times Safari just doesn't work right on a website (AZ501st comes to mind
) but Firefox works perfectly fine.