Hello - I want to correct what Asyn has been saying about leaving that statement on top of Options and Settings. With that message present and Avast having control over Firefox Settings, you DO NOT have complete control of Firefox or your Settings Options. Try this - go into Privacy and Security and try to Manage Data to delete a site's cookies and data. You can't. I'm sure there are other Options you can't access. I just found this one and searched for ways to get rid of Avast control of my browser and removed it
Avast is overstepping with it's control of Firefox. Firefox Quantum also does a better job of protecting me online than Avast has ever done.