Are you not using the Firefox package from your distro's repo? If you were, it doesn't check for updates and I've never in all my years had it load into a new p

Are you not using the Firefox package from your distro's repo? If you were, it doesn't check for updates and I've never in all my years had it load into a new profile after an update. It sounds like you were using the official binary not from your package manager, which in most cases you really shouldn't do that.