It is possible to keep Firefox 2.0 installed for everyday use and run an alpha (or beta) version of at the same time. They each need to use their own Profile though. I've always found some difficulty in setting things up initially. What can happen is that when the alpha/beta version starts up for the first time, it grabs the existing Profile and disables the extensions (because they are incompatible).

Creating another Profile and directing the alpha/beta version to use it on startup (in the Profiles Manager) overcomes the difficulty. Once this is done, the extensions in the stable version's Profile can be re-enabled again. I think this difficulty can be avoided if an additional Profile is created before installing an alpha/beta version of Firefox.

A perhaps better way of running two versions simultaneously is to start each version of Firefox (alpha and stable) via a couple batch files. Instructions here (used this myself).

I don't think I'll try the alpha version. There is some satisfaction knowing that the cutting edge of Firefox is installed but basically, all it means is that I'll have two versions of Firefox. One that works properly and one that might not. Maybe I'm losing my curiosity and enthusiasm

. However, for those who like to take part in feedback over at Mozilla, or just keep abreast of developments, installing and running alpha/beta versions might be interesting and worthwhile.