For me, using Firefox in Linux, the steps were:
1. Go to: Settings->Identity
2. Enter a desired username
3. Answer the question, "Why do you wan this name?" in the text area with a snarky answer.
4. Hit the "Request" button.
Discussion
Now that I've completed the following steps ...
5. Copy the desired username, including "@oregonbitcoiners.com".
6. Go to: Settings->Edit Profile
7. In the "Username" text field, paste your username from step 5.
8. Press the "Save" button
... I should be posting to the right place?
Now my profile in Nostr is screwed up. Fucking lame.