Dev-Info:
1. Avast version X is released, https scanning works for the current version of the browser(s)
2. A new version of the browser is released - with internal changes that prevent Avast https scanning from working
3. Avast version X+1 is released, with updated code to make https scanning work again
There's no way to avoid that (it's happening because there's no "supported" way of scanning browser traffic, i.e. no API - so WebShield, and especially https scanning, has to rely on some internal stuff of the browsers). So yes, Avast supports HTTPS scanning - by updating the code and releasing it as a new version.
So I have to repeat again - the only way to stay as safe as possible is to use the latest versions of the program. If you stay on an older version, you are at risk that some features stop working (because of changes in 3rd party software, i.e. out of our control), the antivirus may not be effective against latest threats (of course the antivirus core responds to the latest development in the world of malware in each version - so older version may not be able to "see" some things), and you may be vulnerable to some security bugs in the antivirus itself (which again we fix once we learn them - and the fix is released as new versions).