If you are in need to run multiple versions of firefox in you PC, such as having both 2.0.0.14 and 3.0b5 at the same time, then this is basically how you do it.

You can get the latest beta version from here, which is 3.0 beta 5 by the time of this writing

1. On your Windows, Click Start > Run (or press Windows Button + R) then type in "Firefox -P" then press Enter.
   


2. On the new window click "Create Profile" and on the next window click "Next"
   


3. Type in your profile name. In this example we use "erasparsa" and click "Finish"
   


4. You'll notice that your profile manager now has two different profile.
   


5. Right click on your current firefox shortcut, and on the target field add the following line "-P "default" -no-remote", click OK
   


6. Install your other version of firefox but do not tick the Launch Firefox now checkbox
   


7. Right click on the installed firefox shortcut, and on the target field add the line similar to step 5 but replace the default with the name of the newly created profile, which in this example would be "-P "erasparsa" -no-remote", click OK and you are ready to go.
   


8. Should you need more then two versions then you basically create a new profile for each installation, and modify each program shortcut to match the created profiles

• -no-remote Enables Firefox to run with multiple profiles; used with -P. Firefox 2 and later.
• -P "profile name" Starts Firefox with a given profile name (profile name is case sensitive).