Affected versions

• 67.0.b10, 67.0.b11(snap), 66.0.3, 68.0a1 (2019-04-15)

Affected platforms

• Windows 10, macOS 10.13, Ubuntu 16.04;

Steps to reproduce

1. Launch Firefox;
2. Access the following link:
   https://rawgit.com/dadaa/3b73f847427025b51ba1ab7333013d0c/raw/77f3f0bb884875a179c3407f73bf8a8dd54751c9/doc_simple_animation.html
3. Open DevTools, Inspector - Animations tab;
4. In the inspector section, click on the <ball negative-delay> div;
5. In the rules section click to modify the animation second value;
6. Increase the value of the timer adding extra numbers (ex: 10s to 10000000000s or more);
7. Revert the value to the initial one.

Expected result

• the value is updated;

Actual result

• the animation is no longer selected in the Animations tab;

Regression range

• Introduced with the new animation inspector;
• Potential regressor: bug 1445825(new anim. inspector), bug 1480027(fix for a reported issue);
• This scenario was not covered by the initial bug since the inspector became blank;

Additional notes

• attached recording with the issue;
• as per the attachment, on invalid values the element is selected again but for exaggerated values it's not working.

Thank you for reporting the issue, Cristi!
I could reproduce it.