Firefox was telling me that, “Avast! Online Security could not be verified for use in Firefox and has been disabled.” The Avast! program stated it was up to date so I could not fix it that way. It occurred to me there should be a place to download the plugin separately to reinstall it and thereby fix this, so I went searching… and could find so much as a mention of the thing on Avast’s website, much less a “fix it” link. I ended up just reinstalling Avast and it seems to be working for now anyway, but why is there no way for us to address the plugin if we ever have issues with it that doesn’t involve needlessly reinstalling the entire program again? Does it exist somewhere that I just couldn’t find? We really need to be able to uninstall and reinstall the plugin independently of the main program. If this isn’t already an option somewhere, it needs to be.
There is no need to uninstall/install avast.
You can remove/add AOS like all other components.
control panel > software > avast > change
Avast 2016: Manage program components in Avast Antivirus setup configuration
https://www.avast.com/faq.php?article=AVKB96#artTitle
Why not create a sticky topic in this forum pointing the above. Might help the newbies.
If you create a Sticky for every problem someone has, you would have a problem getting to currentg questions and answers.
There are already too many stickies. 
+1