You can mark emails as not junk so that next time instead of going into the junk folder they are sent to the inbox. 

Do this by going to your Junk folder, selecting the email and clicking on 'Not Junk'. 

In addition to this you can also add the senders email address to your white list address book. 

To add an email address to your white list inside Mozilla Thunderbird please follow the steps below:

1. From the menu select Tools  - Account Settings

2. Select 'Junk Settings'

3. Make sure there is check next to 'Enable adaptive junk mail controls for this account

4. For the option 'Do not automatically mark email as junk if the sender is in:' select the address book you want to use as a white list. 

Any contacts in the address book will not have their emails marked as junk. 

Please note: you can add contacts to your address book from the email message directly.  Just right click on the email itself and click on 'Add to address book'