When i using whitelist mode, this add-ons sometimes mistakely chages my UA for site not on the list. This happens occasionally and triggers Google's security check which warns me that there might be suspicious / mailious behavior in my PC. (i gauess reason would be they find me using different browsers with same cookie in a short time) I confirmed that both fake UA and real UA appear in the Gmail's "recent activity" within short minutes. Oh, this problem is already reported by someone to the github repo: https://github.com/ray-lothian/UserAgent-Switcher/issues/191