Hello there emmrys. We have read your message. We try to help you. Greetings Firefox Volunteer.

Hello there emmrys. That is called unique indentifier. -What is UID, IUID, UII? The Defense Procurement and Acquisition Policy offers some key definitions that clarify the differences between UID, IUID, and UII. UID/IUID: “A system of establishing globally unique and unambiguous identifiers within the Department of Defense, which serve to distinguish a discrete entity or relationship from other like and unlike entities or relationships. (Ref: MIL-STD-130N Change 1).” UII (unique item identifier): “A globally unique and unambiguous identifier that distinguishes an item from all other like and unlike items. The UII is derived from a UII data set of one or more data elements. (Ref: MIL-STD-130N Change 1).”- Thunderbird has the uid file stored in popstate.dat http://kb.mozillazine.org/Popstate.dat Do you have a good antivirus on your system? http://kb.mozillazine.org/Files_and_folders_in_the_profile_-_Thunderbird http://kb.mozillazine.org/Profile_Manager There are several answers to this question. A good one is erase your profile and Thunderbird and start a new one. Please look carefully whether you have installed a recent lightning add-on, this will also be mentioned when reinstalling. I have a question? are there any other symptoms on your computer machine such as lost emails or the like? Greetings Firefox volunteer.