Evidently, this has not yet been implemented for the master password change form.
As a work-around of sorts, you can create a vault item in your browser extension, which uses two custom fields with the names newMasterPassword and masterPasswordRetype, respectively, with the values of both set to the new master password. Set the URI to https://vault.bitwarden.com/#/settings/security/change-password, and URI matching to “Exact”. A screenshot is shown below. Now, you should be able to auto-fill Bitwarden’s master password change form after viewing the new master password that you entered into the two custom fields.
