Hey there! I totally get how frustrating it can be when you can't log in even though you're sure about your password. Let's try a few things to sort this out. First, make sure you're entering your email and password correctly, as sometimes typos happen. If that's all good, you might want to reset your password just in case. Go to the Thunderbird password reset page and follow the steps there. If you're still having trouble, it's a good idea to clear your browser cache and cookies. Sometimes these can cause login issues. Give these steps a shot and let me know how it goes! If you're still stuck, we're here to help you figure it out.