Have you asked yourself how they got there? You're sort of going at the symptoms without thinking through the underlying problem. I think that you may have imported your address book from somewhere else, or maybe you have edited it in an editor that doesn't support Unicode. There is no search-and-replace tool in Thunderbird's Address Book, so you'll almost certainly have to export, edit and import to fix this. If you export to a CSV file then you should have no trouble, if the funny characters persist, in finding an editor that can do a global search-and-replace. And make sure, when you're done, that the CSV file you write from your editor uses Unicode encoding. ISTR that Excel is spectacularly unsuitable for writing the required Unicode format. If you have to use Excel to check the contents, use a capable editor such as Notepad++ to re-write the file in Unicode encoding.