@Alievitan
I tried both Aurora and Nightly but was told that Avast didn't support either browser so I uninstalled them.
Not supported and cannot use are two different things. Avast is just saying that they cannot guarantee that Avast and Firefox with the features and be conflict free with any version other than stable b/c the code changes frequently.
With that said, it is easy to set up all channels of Firefox (stable, beta, aurora, nightly) in different directories, different profiles, and even run them at the same time if you want. You can set up Mozilla sync so that whatever channel you currently use, you will always have the same history, addons, etc.
I have set all four channel for testing purposes, so when new features come out, I go the relevant channel then see what is it about. I usually stay in stable channel, but the beta channel right now (Firefox 18) incorporates a new javascript engine call ionmonkey, probably the best singular improvement since FF 4 was released, so I am putting it through it paces. And like i posted before, all the Avast realtime stuff including scriptshield works with Firefox all the way to nightly so you can currently use any channel and get all the avast features, and be conflict free as far as I have seen.