Hi,
There’s a previous answer to this question over here: https://dev.twitter.com/discussions/15736.
The fade was disabled because it caused memory usage problems in Firefox, and since that old widget is being retired as part of the API v1.1 changes in a few months, we chose not to reimplement the animation.
What scale dimensions are you trying to achieve with the new widget? Have you seen the updated documentation with new options for width, height and chrome control? https://dev.twitter.com/docs/embedded-timelines
Ben