Use at your own risk.

The file you need is here:

Index of /pub/mozilla.org//firefox/releases/latest-3.6/mac/en-US

Click on Firefox 3.6.16.dmg

When its finished downloading, double click on it and it will expand.

Drag Firefox onto your desktop

Rename the icon to Firefox36 or Firefox4iCrew or whatever just so you don't get it mixed up with the Firefox (latest version) that is already in your applications folder.

If you want to make things slightly easier you can now create a shortcut/alias of the file you just renamed and then drag it to your dock.

Drag the renamed program icon to your applications folder.

Try using iCrew with Firefox 3.6

Use at your own risk.

Not tested at all and done totally from memory because I am too lazy to startup my mac laptop and I use Windoze at home.