Windows?

Have you added the new outlook.com account into Thunderbird yet?

If not:

• Go to Tools|Account Settings
• In the Account Settings window, go down to the button at the bottom, click it and select "Add Mail Account".
• Follow the instructions. Use "Continue", not "Get new address"! ;-)

I expect that this new account will automatically become the default. If not:

• Go back to Account Settings.
• Select your new account.
• Click the button at the bottom, and select "Set as Default".

See the attached image; your button may have a different label. Confusingly, it shows what you last did with it, so it is somewhat unpredictable.

Oh, and it is not a good idea to publish email addresses on websites. I suggest you edit your first posting and remove the account names. (I don't have the authority to do that for you.)

How do I edit out the addresses I posted?

Isn't there an "Edit this post" option for you?

There's no edit button

I have asked an admin to look at this.

I found a button to edit with.