We use Gmail as our primary email account. We import that into Thunderbird. We have many folders and subfolders in Gmail which we could always see in Thunderbird. Most of those folders have suddenly disappeared from Thunderbird. We can still see them in Gmail so we know that they still exist. We are not aware of any changes that we made in Thunderbird to cause this. Any assistance or suggestions with this matter would be greatly appreciated. If it makes a difference, we use Firefox for our browser and Linux for our operating system. Thank you.