Many here have had the problem of Norton Password Manager Vault not opening in FireFox. Recently, (Sept. 2023), I had the same problem with both of my laptop computers (one is on Window's 10 and one is on Windows 11), but I found a solution! First, I uninstalled Norton Password Manager extension in FireFox (right click on the icon - uninstall). Then I opened up My Norton application on my computer and went to the Password Manager from there (open Device Security - Internet Security - Password Manager) and re-installed it. Now the extension works in FireFox and I see the yellow icon (for Password Manager) on my toolbar (upper right) and it works on both my computers. I hope this is helpful to others.