Comment by stankot

I've figured it out. The error means that this call fails:

    const animation = animationElement.getAnimations()[0];

As Firefox supports `getAnimations` since 2020, I figured something else is messing up with it. I've tried to enable "reduced motion" in the system settings and it broke the animation!

It is because I had force-disabled all animations on the site when this option is enabled.

I patched it, it should work now. Thank you for your help!

EDIT: typo

EDIT2: I also added simple error handling to display a message if parsing the animation fails.