Possible Duplicate:
How to install Firefox 3.6 and 4.0 in parallel?
Is there any way to install Firefox 3.6 in Ubuntu 11.04? I need Firefox 3.6 because Firefox 4 does not support Google Gears which is required for Offline Gmail and Google explicitly stated that they are not going to update Gears for Firefox 4.
You can download it from Mozilla site, extract the tar.bz2 file somewhere in your home and execute the firefox file inside it. See my tutorial for step-by-step instructions.
I would recommend using a separate profile for the 3.6 account. You can use the Mozilla's Profile Manager to create profiles and start different versions of Firefox.
