From Xojo Documentation

Read-Only Property (As Boolean )
BooleanValue = aWebAnimator.OpacitySupported

New in 2010r4

Supported for all project types and targets.

Returns True if opacity animation is supported by the web browser. If False, the Opacity method does nothing.

Sample Code

Only change the opacity if the browser supports it:

If Animator1.OpacitySupported Then
Animator1.Opacity(ImageView1, 0, 4)
End If