I'm used to manually update firefox browser on my windows 10 pc, everything was fine before, but I found a strange situation about two weeks ago, the situation has occurred twice so far -- For the previous version, I manually download update in settings, firefox browser can be restarted but not updated after clicking restart firefox button, and an error notificaion ''firefox being updated by another instance'' appeared instead of 'check for updates'' button, then the update process started when I exit firefox browser and reopened it. For the latest version, the strange situation occurred again when I tried to manually update firefox browser, the only difference is that I don't see the error notification from last time. Why does the situation happen? Do it cause any risk? How can I fix it?