I just switched on my PC, opened Firefox and got a message saying "sorry we could not restore the pages" or something similar. And then a row of windows opened from each one of the extensions that have been deleted saying things like "we're sorry to see you go" "we hope you come back" and so on. On double checking were extensions like eosia, momentum, mendeley, notion, freedom etc. all gone, and not for my choice. I disconnected my account, checked my laptop but before i could block sync, all extensions started deleting themselves there as well... according to AVG premium, no malware or virus was detected...