Well, even if you find a tool that requires a password to start Firefox, that wouldn't solve the problem because the data is still sitting there on disk for anyone to access. Are you able to use full disk encryption on your system? If not, a possible option is to put your Firefox profile folder ([[Profiles - Where Firefox stores your bookmarks, passwords and other user data]]) into an encrypted file and access it as a folder on a virtual partition. One tool for that is VeraCrypt. I haven't tested that setup myself, but there is a mention and a couple links in the conclusion of this article: https://medium.com/@pablo127/encryption-is-it-worth-to-encrypt-your-drive-378fc9abe1ef It's also one of the methods mentioned as providing Strong protection here: http://kb.mozillazine.org/Protecting_the_contents_of_the_profile_-_mail If you try that or other things, please let us know what you discover.