Some settings in the ProtonMail web client require entering the user’s password in a modal. If Kee enters the password into the password input box, the form is permanently disabled. If I start by manually typing a character to enable the submit button for the form, and then tell Kee to enter the password, the submit button becomes disabled and nothing can re-enable it.
I’ve used Kee on hundreds of websites and this is the only time I’ve experienced this issue. It’s also the only time I’ve used it to fill in an Angular Modal dialog, so that might be the source of the issue somehow.
If you don’t have a ProtonMail account, the basic account is free.