Because FF6 is not compatible with latest Avast?
Wrong, it is the webrep (not avast) which doesn't work with firefox 6.0, but that in all honesty is no big deal as the webrep isn't a security based feature.
- The fact that you don't see the WebRep or it doesn't work with the current firefox version, doesn't lessen the avast protection. You still have the Network Shield blocking known malicious sites and the Web Shield pre-scanning http content before it is displayed/run in your browser.
The WebRep is purely reputation based on avast user input. Later when the avast! virus labs start inputting information of detected malware, etc. into the webrep database, then it will be more of a security feature than just a reputational tool.