Hi,
This changed in https://bugzilla.mozilla.org/show_bug.cgi?id=1734195
When prefers-reduced-motion is set to reduce, we now use simplified highlighters to avoid creating flashing effects on the screen which can be disturbing for some users.
Although I can imagine not everyone enabling prefer-reduced-motion had this issue so it makes sense to make this configurable.
Edit: Filed https://bugzilla.mozilla.org/show_bug.cgi?id=1817639