They are unfortunately uncommon in web forms for anything not business-facing but are very common anytime the user might be associated with a business as business users often have extensions.It is currently a bit harder to handle this on the web in t...
This is the sort of thing I've been wanting to do myself, but cool to see Mozilla building this! One feature that I think would be helpful: since you can only have one phone number, why not let people generate (long-ish/random) extensions per-contact...
