Mozilla Thunderbird password

[Harold]

I changed the password on my g-mail account thanks to Heartbleed.

Now at random times Mozilla Thunderbird keeps asking me to enter a password.

I enter it and check the box to retain it in master password.
I do mot normally use a master password, so it has never really been set up.
In preferences | security | passwords | Saved Passwords, I can push a 
button labeled "Show Passwords" and the new password is shown.

I checked in both preferences and account settings and I can't seem to 
find the spot to change the password.

I would hate to have to delete and create a new account just because I 
am missing something.

Harold