I am wondering if Avast Free screens for malicious websites and give you a warning.
I use Mozilla Firefox which has a setting option to block attack websites and website forgeries.
If Avast does much the same as Firefox, I don’t think that I would need both filtering and slowing down my browser. I would choose Avast to do the job.
Leave the firefox anti-phishing/secure browsing on, a) it doesn’t actually scan anything but check the URL against a known sites list and b) they don’t conflict and it doesn’t hurt to have protection in depth in this case.