All doorhanger elements cannot be focused using "Tab" key

[Softvision-CristinaBadescu]

[Affected versions]:

• Firefox 60.0.2
• Firefox Monitor 0.01, All Branches

[Affected Platforms]:

• All Windows

[Prerequisites]:

• Have a clean Firefox profile with the latest Firefox Monitor installed.

[Steps to reproduce]:

1. Open the Firefox browser with the profile from prerequisites.
2. Navigate to a breached website (eg: https://126.com).
3. Click inside an empty space of the doorhanger.
4. Press the "Tab" key once.

[Expected result]:

• The first element of the doorhanger is focused.

[Actual result]:

• No element is focused.

[Notes]:

• This issue is also reproducible for the feedback form checkboxes.
• This issue is not reproducible if the user previously focused the "Arrow" button (by clicking it).
• This issue is not reproducible if the user previously focused the email field.
• Here is a screen recording with this issue:
  

[nhnt11]

Interestingly this works if one clicks on the anchor image. Not sure what to do here...