What component of Comodo FW you want to exclude from monitoring Avast. You have shellcode injection exclusion under Advanced Protection Configuration > Miscellaneous Settings > Exclusions "In case you want to exclude certain applications from shellcode injection protection". Other than that, what you have left is to make sure all Avast process and services are listed in your HIPS rules as "Windows System Application" meaning freely allowed, in case you have HIPS enabled. If HIPS is disabled then the FW traffic rules and the rest it's the same just rules.