you installed it wrong. on mac os or windows, you download a program from /its/ website and run /its/ installer. on ubuntu (or pretty much any linux distribut

you installed it wrong. on mac os or windows, you download a program from /its/ website and run /its/ installer. on ubuntu (or pretty much any linux distribution or *bsd), you look to your vendor for pre-compiled packages of this software (linux distributions using dpkg, rpm, whatever, bsds using ports/pkgsrc/packages). so on ubuntu you run whatever package management utility comes with it and tell it you want to install firefox 3. it fetches a package built by another ubuntu user and installs it. of course, you can manually download/configure/compile/install any of this software, but using pre-compiled packages is usually much easier, faster, and integrates better with your other installed software.