I use firefox and https just fine, I'm not sure what particular "known issue" you're referring to. I'll try and offer some advice if I can though.
Perhaps lets start with the basics, like Windows version, Firefox version, Avast version etc. Do you have any screenshots you can share? Is it happening on all computers or just some? All https sites or just a selection of sites? Do other browsers have the same problems? Have you contacted support for advice?