The title says it all really. I have been experiencing this in the problem, which I believe is still related to browsing HTTPS pages.
Browser Firefox 41.0.1, avast free 2016.11.1.2234 on XP Pro SP3.
I can be browsing quite happily and all of a sudden I can't load HTTPS pages, I see this in these forums and other HTTPS sites.
I started by disabling HTTPS scanning, but at times that didn't appear to work. Now I tend to just shut down the Web Shield (10 minutes option), but almost immediately enable it again. Now browsing those same pages is restored.