[[Vista 32-bit/Firefox 4.0 beta 11]] At first I updated from v.5-something to v.6.0 (free) using the built-in updater in v.5. All seemed fine until I discovered the old Avast 5 link remained in my list of software in the Start Panel - and that link launched v.6. In the interest of leaving well enough alone, I didn't fuss with it.
But about one day later I noticed the WebRep toolbar icon had gone gray - oh no, my long-awaited favorite new feature! I tried disabling it in Firefox Add-ons, thinking I could re-enable it in an effort to jumpstart it again. But it vanished altogether from the list of Add-ons.
So I used the Avast 6 installer to "change" my install. That made no difference WebRep-wise, so I uninstalled the original v.6 (which seemed a little messed up anyway) and reinstalled using a downloaded standalone setup package. This did put WebRep back into the Firefox Add-ons, with the expected toolbar icon. Nonetheless the toolbar icon remained grayed out.
Then I googled the problem and found a few threads on this forum indicating the WebRep server had been down. Even though one entry - dated yesterday - indicates the server problem had been resolved, it doesn't seem to be, here in northern California anyway. Haven't seen a sign of life in that toolbar icon.
Other than the semi-messed-up first install and these WebRep problems, Avast 6 looks excellent to me (as did v4 and v.5). Can't wait for 6.1.