By the way, at the U3 Software Central description about Mozilla Thunderbird there is a lapsus cálami: "Automatic Updates The Software Update feature makes it easy to get the latest security and feature updates to Thunderbird. Mozilla Firefox for U3 automatically notifies you of available updates and allows you to download and install them. Running the update process requires at least 40mb free on your U3 device and may take 5 minutes or more to complete." Mozilla Firefox is NOT Mozilla Thunderbird. :P One more thing: I think there is not need to have at least 40 Mb free, 20 Mb are quite enough and after downloading the updating, the update-installing process usually takes less than 4 minutes.