You can download Firefox. Pick the Mac version, then copy the DMG file to your iBook. It will open there, and you can drag the Firefox app to anywhere. Safari unfortunately will come in an install package, and you are lacking the Installer. In 10.4.x, it is at /Applications/Utilities/Installer.app
Do you know anyone locally who uses a Mac? Any 10.4 PPC install disc should be able to provide a usable Applications folder. Even a dedicated install disc for a different Mac model. You'd copy the Installer across first, then manually run the applications install package. Or copy the Applicatons folder from an existing install.