Running Firefox 3.0.19 and 3.6.x simultaneously?

Is there any way to run Firefox 3.0.19 and 3.6.x simultaneously? I think it's possible by allowing multiple instances of Firefox, but I might shoot myself in the foot that way, so I'm looking for a way that only allows me to run a single instance of each version at the same time.

I need this, because VMWare Server console plugin requires the older Firefox version, and VMWare has made clear that they are not going to bother about updating their plugin.