Browser version-specific performance variations

[twitwi]

In most presentations, even for simple animations, some browser versions have a lag/delay when pressing the right arrow key, e.g.:

https://twitwi.github.io/Presentation-2017-01-04-saintelyon-deeplearning-workshop/#plan

• laggy in Firefox 50.1.0 default on mint
• slick in Firefox aurora 52.0a2 (2017-01-07) (64-bit)

but this has been true for a long time (when aurora was 50 or even below).

To be investigated.
Any help from an expert profiler is welcome :)