I have noticed an unusual problem with Firefox showing a layer in an imported Illustrator artwork as detached from the layers in front of it, that is, the Illustrator layers, which are all on the same Animate layer. Only happens in Firefox, but not on all machines.
In Chrome, no problems:
This is what it looks like in Firefox:
In Animate that eye graphic is on the one Animate layer. The graphic is comprised of multiple layered graphics, all imported as a single layer object from Illustrator.
If I pull that graphic apart in Animate, the round iris that appears to pop to the top in Firefox, doesn't look like that. Rather the iris is shaped at the top, not round.
Adobe Illustrator artworks tend to be very complex, containing lots of features that are not supported either by Animate or the canvas.
So I always prepare the imported files trying to remove as much as I can things like the masks generated by the imported process, or change the blending modes back to normal or edit the gradients.
Not to say the that this preparation stage is very important for performance gains.
But if it's not practical to edit the imported arts, you can always consider converting them to bitmaps.
I hope this helps.
The point is to simplify the imported artworks.
You have to remove all kind of features that may cause browser issues, like blending modes and some filters options.