What are you trying to save? All you should need is your Thunderbird profile. https://support.mozilla.org/en-US/kb/profiles-tb This will save all your account settings, messages, folders, address books, filters, extensions and add-ons etc. Saving ''everything'' is actually easier than trying to pick out just the address book data. If you must, then you're looking for files with a .mab filename extension. Two of them, ''abook.mab'' and ''history.mab'' can be just copied into your new profile. These represent, respectively, Personal Address Book and Collected Addresses. Others, which will be user-defined address books, will have names such as ''abook-1.mab'' and will need to be imported into your Address Book, using this add-on: https://nic-nac-project.org/~kaosmos/morecols-en.html Are you satisfied with an OS that requires periodic rebuilding? There ''are'' alternatives. ;-)