Possible Duplicate:
Install Firefox 4 Beta alongside Firefox 3.6?
I am doing web development and I have Firefox 4 and I need to test in Firefox 3.6 with Firebug. Can I install both Firefox 4 and Firefox 3.6?
Possible Duplicate:
Install Firefox 4 Beta alongside Firefox 3.6?
I am doing web development and I have Firefox 4 and I need to test in Firefox 3.6 with Firebug. Can I install both Firefox 4 and Firefox 3.6?
You can run different versions of Firefox, (among other apps) in your browser, without downloading them, using Spoon. Give it a try...
Bring your apps to the cloud - Spoon virtualization lets you run desktop apps anywhere with no installs... The Spoon plugin is an extension to your browser that lets you run apps from the Spoon web site and other Spoon Servers. You need to have the Spoon plugin to run Spoon apps.
Note: I am not affiliated with this product in any way, shape, or form.
You don't have to install both Firefox 4 and Firefox 3.6. Get the portable version for the release you need: http://portableapps.com/apps/internet/firefox_portable/localization
There are more complicated solutions using the Profile Manager, but running a portable version is much faster.