css animation on “content:” - works on chrome, doesn't work on Safari and Firefox

Just found out about this ...

https://stackoverflow.com/questions/40027799/css-animation-on-content-doesnt-work-on-safari-and-firefox

.. that post has a really simple example, showing the thing.

Might be relevant to be added to caniuse.