Avast is blocking Firefox sync

Avast Free Antivirus / Premium Security
1

Steps to reproduce:

  • make a fresh intall of Firefox with Avast installed

  • log in to your Firefox sync account with your email and password

  • you can wait or force a manual sync

  • nothing will happen

  • you can check errors at: about:sync-log - especially “TokenServerClientNetworkError”

  • close Firefox

  • turn off Avast for 10 minutes

  • start Firefox

  • choose manual sync

  • it will sync all your bookmarks, extensions, etc.

Tested with newest Avast, Win 10 64bit, Firefox 41 beta

2

Ok, found out that it is a much complex problem. Some https sites also doesn’t work with sec_error_bad_signature or ssl_error_bad_mac_read errors.

The solution is here: https://support.mozilla.org/hu/questions/1075167 - in short: Uncheck the “Enable HTTPS Scanning” option in Avast.