Have you let them use your computer before? Does your Firefox profile sync with other, less secure devices? Try removing the saved logins and see if they reappear - this will probably prove their recent access. If you think Sync may be the cause, read the following articles: Sync logins in Firefox desktop Sync custom preferences Suspicious activity on my Firefox Account Disable Firefox Sync

Hi, no, no-one has physical access to my locked computer/office. A couple of the MSP techs have remoted in before to do service while I supervised but they didn't fill out any forms that would have cause an autofill memory and even stranger - one of the names is of their accountant who has never had access for any reason. I have never installed Sync. Thank you for your ideas, I'll review them.