Yeah. My Avast upgraded today, and I came on here because I had the same issue as you. Same setup, Vista 32 bit sp2, Firefox. It was actually stopping some sites from loading completely, preventing my main email address from letting me logging in, and blocking a lot of content, which was pretty problematic (until I tried turning off the shield and realized it was an Avast issue). Turning off HTTPS scanning seems to have fixed the problem, though. Hopefully there will be a fix soon.