"about:" pages can be added to FBC, the titles are displayed as empty in the list and they can't be removed

[gpalko-SV]

• Facebook Container Version: 2.1.0
• Affected platforms:
  - Windows 10 x64
  - MacOS 10.15
  - Ubuntu 18.04

Steps to reproduce

1. Add Facebook Container 2.1.0 to Firefox
2. Open any about: page in new tab (e.g about:support)
3. Allow the page in FBC
4. Click the Facebook Container icon and select "Sites Allowed in Facebook Container"

Actual behavior

1. The page is added to list but the page title is displayed as empty
2. The page remains in the list after removing it from FBC
3. A new entry containing the add-on UUID is added to list after every Remove attempt

Expected behavior

1. The page titles should be displayed in the Allowed list
2. The about: pages should be removable from FBC
3. No new items should appear in the allowed list after remove operation

OR

The user should not be able to add "about:" pages to FBC

Notes

See the attached screenshot

[maxxcrawford]

IMO I don’t think about: pages should be allowed inside the container. I recommend we handle them in the same way removing default Facebook domains (Facebook.com, Instagram.com, etc.) is not allowed.

[gpalko-SV]

Verified on build 2.1.0-rc2, that about: pages cannot be added to FBC.