Is there are any way to run Firefox 4 and Firefox 3.6 concurrently?
You can try portable Firefox. I have installed Firefox 4 and use Portable Firefox 3.6.
Try using Spoon. http://www.spoon.net/home.aspx
You can try also a great collection from Utilu: http://utilu.com/UtiluMF/
If you're on Mac OS X MultiFireFox is an option.
It is not clear from the question which system you are running firefox.
If this is firefox on linux you can simply download that tarball for each of the versions that you wish to use. Then you can untar to whatever location you want. I suggest :
Thank create a couple of symbolic links to do your job in /usr/bin/ with the commands
ln -s /opt/mozilla/firefox3.6/firefox /usr/bin/firefox ln -s /opt/mozilla/firefox4/firefox /usr/bin/firefox4
You can also be creative with the naming.
Just download the versions that you want. Install , they automagically go into different directories. Then go to the installation directories and make shortcuts to you desktop.
Here is a link for older versions:
then you should use FF profiles for each of these versions.
once you have create the profiles e.g. A and B you can set them in the shortcuts to start with:
firefox -P A firefox -P B