I have used Thunderbird for many, many years. Never had a problem until lately when I moved to a new computer. I now have a problem with "address book". Problem could be either import or export or in the use of address book. The problem may have started when I moved the address book from my old computer (Win 10 pro 64 bit, Thunderbird 102.6.1) to a new computer (Win 11-Pro, Thunderbird 102.7.0, 64-bit) Old computer is OK, new computer has error. Error: Start to display "inbox" then click -> Tools-> address book. Address book displays, BUT display in on half line spacing, not the normal full line spacing - if correct data displays correctly. In half line spacing, lines overlay each other. Also I can not modify a contact and I can not add a new contact. I have only one profile, no extras on Thunderbird. When I click on a contact that display incorrectly I get a grey box (almost the whole display) and I can not type into that box. Can not close that box, can not go back, can only close tab. Tried on web to backup address book. In command prompt (the old DOS) with current directory set to: "C:\" typed "dir *.mab /s". Result: "file not found". I can not find any "mab" file anywhere on C:. (Windows is installed on C:. One problem you probably know, when Thunderbird is updated, help files on Web are not updated. (Example web states to go to "run", can not find "run" on Thunderbird menu). Went through many sites on web, can not find file containing address book and can it not back it up, can not fix it, can not where it is. Looked at profile at What went wrong? I am out of luck. My background: Worked on PC since Windows 3, I am comfortable on PC/Win, repair PCs, etc. Sorry to bring you this, can not figure this on out. Gerry