I just installed Firefox on a newly upgraded Work laptop & tried to sign-in to Sync. I am getting the 'The request was blocked for security reasons' error. This page provides the "Troubleshooting" information for the same : https://support.mozilla.org/en-US/kb/accounts-blocked. I have not received any mail from Firefox; searched through all my mail folders Inbox, All Mail, Spam, Deleted. I couldn't find any mail regarding 'confirmation' of my account from Firefox around the time I have attempted to add Firefox Sync. This is a new installation of Firefox , just opened (after a "reset") & is in "factory" condition.