Running two separate verions of firefox on linux

In many cases of active web and software usage you might need to run an older version of a web browser. In this case I needed a to run Firefox 8 and I didn't want to remove my current version. here is what to do:

1- Create a separate directory and move to it:
$ mkdir /home/mzakaria/opt/firefox8
$ cd ~/opt/firefox8/

2- go to Mozilla FTP server at ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/. and look up the release you want

3- get the folder using wget:
$ wget ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/8.0/linux-i686/en-US/firefox-8.0.tar.bz2 (I got the one with i686 b/c I am using a 32bit machine, you can check that with the command uname -m; it will give you i686 if it was a 32bit)

4- untar the package:
$ tar xvjf firefox-8.0.tar.bz2

5-  move the unpacked folder to a folder with the name you chose (in case you are bringing more than one release)
$ mv firefox firefox8

6- Each version needs a separate user profile — otherwise, it won’t be possible to run them simultaneously, and worse, it might break the default profile which is used by the system version. For our version:
$ firefox -no-remote -CreateProfile firefox8

7- That's it! change to the folder again and run it:
$ cd firefox8/
$ ./firefox -no-remote -P firefox8

Notice that this will create a completely separate browser, you might want to move some bookmarks or certificates.