Your addresses are stored in files on your harddrive. If your colleagues are also using Thunderbird at a similar release level, you could share the actual files with them. But my guess is that isn't your intent. Another low-tech approach would be to extract your address book to a csv file and email that to them. If you want yourself and colleagues to share live updates, then you need to get your addresses online, such as carddav with a google account that each person sets up individually. But that takes time for each individual. There is no simple, quick, solution. I suggest going with the csv file for now, and then reassess with colleagues on how you all want to proceed long-term.