Open the Bitwarden extension, and click (under the small 'servers' label) bitwarden.com, changing it to self hosted. This will bring up a dialog. Enter "https://vaultwarden.p0ntus.com" in the server URL, and leave the rest of the fields blank. It should now change 'bitwarden.com' to 'self hosted'.
Enter your email and password, and click 'Log in'.