So, the very first time I use 1password in Firefox with CTRL-\ after booting up, the "enter your password" will not be selected by default. Actually, nothing will be. However, as you type, the selection will jump to the ... at the top left of the screen or it will cancel out and I will end up typing my master password into whatever filed was selected on the web page. I need to remember to hit tab once then type in my password and then 1password will remember to go to the password field by default until I reboot my computer (even if I lock 1password and close all my browser Windows).
My suggestion would be to ensure that the password field is always selected when unlocking 1password.
1Password Version: 8.4.1
Extension Version: 2.1.4
OS Version: Windows 10