Affected versions

• Firefox 67.0b5 (20190325125126)
• Firefox 68.0a1 (20190326002640)
• Firefox 66.0.1 (20190322013140)

Affected platforms

• macOS 10.13.6
• Windows 10 x64
• Ubuntu 16.04 x64

Steps to reproduce

1. Open Firefox and go https://www.facebook.com/ login page.
2. Open the DevTools Inspector.
3. Locate the :root selector in the rules.
4. Remove or edit any property in the above mentioned section (ex.: --fds-black: #000000;).
5. Click inside the Changes tab.

Expected result

• Only the changes are listed in the section.

Actual result

• The changes section is fully populated with all the entries under the rules section (marked as added).

Regression range

• This is not a regression because it’s happening from the implementation of Changes but the behaviour is different. See additional notes.

Additional Notes

• Trying to copy the rules form the [Copy rule] buttons or right click context menu ignores the section and pastes the previously clipboard content (as seen in the attached recording).
• On Firefox 65.0a1 (20181121220101) the same behavior is happening but the list is not populated and everything is enumerated in the same row, only the last rule remains (see this video recording: link).

A reduced test case does not exhibit this issue, so the problem lies in some other interaction.

data:text/html,<style>:root {--foo: 1em; --bar:100%; --baz: 100%;}</style>`