Bugzilla

Based on discussions with Markus, we would like to explore the following revisions to Firefox's scroll physics:

 * For scrolling animations triggered by user input such as keyboard and mouse wheel scrolls, tweak the constants in the current Bezier physics to make the resulting animation's shape more like the native behaviour in Windows applications (including Edge).
    * Chrome has made a similar set of changes described in [this design document](https://docs.google.com/document/d/1A3VmlY3ZR6UtJt3QQ5uuqaCOgPjV6vCMxvkpvPBe0g0/edit).
    * Note that this would be a change in direction compared to our previous plan to switch to a new Mass-Spring-Damper based physics model (bug 1760372).
 * For programmatic scrolling animations, disentangle `scroll-behavior: smooth` from "scroll snap" (the two currently share an implementation, and use a Mass-Spring-Damper physics model, though a slightly different one than the one we were going to use for keyboard/mousewheel in bug 1960372).
    * Switch `scroll-behavior: smooth` to use the same (tweaked Bezier) physics as keyboard/mousewheel. This would address bug 1916760.
    * Keep "scroll snap" using the Mass-Spring-Damper model it's using now.

Based on discussions with Markus, we would like to explore the following revisions to Firefox's scroll physics:

 * For scrolling animations triggered by user input such as keyboard and mouse wheel scrolls, tweak the constants in the current Bezier physics to make the resulting animation's shape more like the native behaviour in Windows applications (including Edge).
    * Chrome has made a similar set of changes described in [this design document](https://docs.google.com/document/d/1A3VmlY3ZR6UtJt3QQ5uuqaCOgPjV6vCMxvkpvPBe0g0/edit).
    * Note that this would be a change in direction compared to our previous plan to switch to a new Mass-Spring-Damper based physics model (bug 1760372).
 * For programmatic scrolling animations, disentangle `scroll-behavior: smooth` from "scroll snap" (the two currently share an implementation, and use a Mass-Spring-Damper physics model, though a slightly different one than the one we were going to use for keyboard/mousewheel in bug 1760372).
    * Switch `scroll-behavior: smooth` to use the same (tweaked Bezier) physics as keyboard/mousewheel. This would address bug 1916760.
    * Keep "scroll snap" using the Mass-Spring-Damper model it's using now.