How to Set Up and Run Firefox 3.0b2 as a Different User in Ubuntu

I wanted to test Firefox 3.0b2 on my computer, but I didn’t want it to interfere with my current Firefox profile or even my current system. I decided to create a separate user and use that user specifically for running Firefox. No, that doesn’t mean that I have to sign out and sign back in as that new user every time I want to use it.  I can run Firefox 3.0b2 under its own user at the same time as all of other programs. I can even run both versions side by side for comparing and testing.

1. The first task is to create a user for our test version of Firefox. Click on the System (Gnome Menu) -> Administration -> Users and Groups.
2. Click on Add User.
3. Type in ‘fftest’ for the user name and choose a password. Then, click OK.
4. Fire up a terminal, su into your new user and go to your home directory by typing the following commands.
   

   su fftest
   cd ~

5. Download Firefox 3.0b2:
   

   wget http://ftp-mozilla.netscape.com/pub/mozilla.org/firefox/releases/3.0b2/linux-i686/en-US/firefox-3.0b2.tar.bz2

6. Extract the archive.
   

   tar -jxvf firefox-3.0b2.tar.bz2

7. Type in this command to tell Firefox not to use an existing session.
   

   export MOZ_NO_REMOTE=1

8. Start Firefox
   

   ./firefox/firefox

9. If you get an error like this…
   

   Xlib: connection to “:0.0″ refused by server
   Xlib: No protocol specified

   (firefox-bin:5160): Gtk-WARNING **: cannot open display:

   …that means that you need to let the ‘fftest’ user launch applications that interface with the current GUI. In order to do that, you will need to fire up a new terminal that is under your desktop user, and type in the following command:

   xhost +local:fftest

   Then start Firefox again.

   ./firefox/firefox

10. You should now see the Firefox start page.
    
    This Firefox session is completely independent from your current version, you can run them side-by-side.
    
    
11. Repeat steps 7-10 to run Firefox 3.0b2 in the future. When you are done testing, just delete the user ‘fftest’.

If you find any issues or problems with this tutorial, please contact me or post a comment.  I always want to ensure that I’m posting accurate instructions.
Reference: http://www.captain.at/firefox-run-different-versions.php