Dweets run significantly slower on certain browsers

Mobile and desktop Safari renders dweets at 33fps instead of 60fps. [This dweet](https://www.dwitter.net/d/10964) can be used to test. Other browsers may be affected as well. #414 may be related.

Start by reproducing the linked dweet (d/10964) on mobile and desktop Safari at its reported frame rate, then compare it with other browsers. Read issue #414 for related context; done means identifying and addressing the cause of the reduced rendering rate and verifying the dweet reaches the expected 60fps where applicable.

Written by the indexing model from the issue text.