Avg 8 stopped updating
All HTTPs sites were rendered broken and I worked for a long time working this out as I did not try any of them before installing avast.
Tried turning off the shields but that did not help.
When you get to the screen that shows the items to be installed uncheck the option to install "Browser Protection".
avast will now be installed without the browser add-ons and you will not encounter this issue.
What I like is the auto sandbox, if you need to or if something is suspicious, Avast will ask if you want to run it in Auto Sandbox, which is basically a virtual setting so no harm is done to your actual system. I suggest you use it with MSE for guarantee to be sure you are clean. I've always found it to work very well and is reasonably fast.