1) Right click the email account
    2) Select "Subscribe" from the pull down list.
    3) A list will popup of all of the folders for that account
    4) Highlight any folder that doesn't have a checkmark in the box to the right of each folder and place a checkmark in the box by selecting the box.
    5) Select "Refresh" from the right panel, then select "OK"

I find that I have forgotten most of what I have learned about Thunderbird. Recently I needed to "refresh" the folder list from one of my email accounts for I had created a subfolder under a parent folder while using the browser to access the email account online. I remembered that I was able to "refresh" the folder list very easily for this happened in the past. I was able to find the resolution in Thunderbird's FAQ/Help, but that took some time. You probably noticed that I quoted the word "refresh", that isn't the correct search criteria for it is actually a synchronization issue. Before you search how to Synchronize folders: 1) Right click the email account 2) Select "Subscribe" from the pull down list. 3) A list will popup of all of the folders for that account 4) Highlight any folder that doesn't have a checkmark in the box to the right of each folder and place a checkmark in the box by selecting the box. 5) Select "Refresh" from the right panel, then select "OK" Although I could use a PC based journal, I would like to have such a journal/note section within Thunderbird so that I can keep How-to notes.