It doesn't work as expected, but I was able to retrieve some contacts, but it only saves numbers.
You have to go to the group info tab > members > search members.

So far, this is the only extension of its kind that's worked for me.

Tested on 8/23/2025. However, the app doesn't save all contacts, only those you don't have saved in your account, and not all of the group's contacts. For example, in a group of 1,013 people, it only saved 508.