Http basic auth support

I saw some closed http basic auth feature requests, I believe they was closed due to implementation of this particular support, however, it seems it's not working for me.

Steps to reproduce

1. Enter the site with http basic auth. For example https://observer.abinet.ru
2. Fill credentials and proceed

Expected behaviour

1. Request to save credentials, like FF password manager does.
2. Search for saved credentials and fill them

Actual behaviour

1. No request to save credentials after login
2. Detected credentials are not filled. However, I'm not sure if it is ever possible - FF dialog is modal, so passman UI is not accessible and if I have different credentials, I'm not sure how can I choose them.

Configuration

Operating system: FreeBSD 11.1-STABLE

Browser: Firefox 52.3.0 ESR

Extensions that might cause interference: uBlock, uMatrix

Passman version: NA

Extension version: 2.0.4

Nextcloud version: NA

Browser log

Nothing interesting here.

Want to back this issue? Post a bounty on it! We accept bounties via Bountysource.

Start by reproducing the reported behavior at https://observer.abinet.ru in Firefox 52.3.0 ESR and inspect the extension's handling of HTTP Basic Auth. Done means determining whether credentials can be saved and selected for Basic Auth prompts, or documenting the browser limitation if the requested flow cannot be supported.