Avast, please get a Firefox “signed” cert for your Mac AV browser add-on. As of Firefox 39, you will need a signed cert to stop the warnings from Firefox add-ons I am getting a warning from Avasts and 1Passwords add-on not being signed in Firefox 40 Beta. If an add-on crashes on startup IE badly coded add-on/malware Firefox will automatically disable that add-on.
Considering the nature of the HTTPS scanning being a man in the middle type of use, Im not sure if it would be possible (Not sure if any CA would issue a cert that can itself be an intermediary cert). But if its possible i’m sure the avast team is working on it.