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The first thing to realise is that Iceweasel is Firefox with a different name, so you didn't have to download Firefox at all - you could simply use Iceweasel.
But if you really want to use your downloaded Firefox, then there are two more things to understand:
1. Filenames in Linux are case-sensitive, and the executable for Firefox is 'firefox', not 'Firefox'.
2. Linux handles file paths differently to Windows. To run an executable in the current directory, you should type ./ before the filename ('.' means the current directory). So the command which you should have typed after entering the directory where Firefox was extracted is:
johnson@johnsonxp:~$ cd firefox
johnson@johnsonxp:~/firefox$ ./firefox
./firefox-bin: error while loading shared libraries: libgtk-x11-2.0.so.0: cannot open shared object file: No such file or directory
johnson@johnsonxp:~/firefox$
johnson@johnsonxp:~$ cd firefox
johnson@johnsonxp:~/firefox$ ./firefox
./firefox-bin: error while loading shared libraries: libgtk-x11-2.0.so.0: cannot open shared object file: No such file or directory
johnson@johnsonxp:~/firefox$
Do you have Iceweasel installed? In fact which desktop/wm are you running? I say this because libgtk2.0-0 is one of gnome's dependencies so should already be installed.
Also why are you installing firefox in your home directory?