We want tab-to-search results to have a slight animation. We should disable this animation when the user has specified prefers-reduced-motion.

From bug 1647927:

We should consider the case of when a user has two engine aliases registered, one of which begins with the other in its entirety. For example, they have Amazon registered as "a" and AliExpress registered as "ali". When the user types "a" we should show the Amazon tab-to-search result. But when they then type "l", we should replace the Amazon tab-to-search result with the AliExpress one. We want to be sure that we don't reanimate the tab-to-search result to avoid annoyance.

Here's a prototype of the animation - https://cloud.protopie.io/p/920a84c715/6?ui=false&mockup=false&touchHint=false&scaleToFit=false&cursorType=arrow

• It uses the photon motion curve: cubic-bezier(.07,.95,0,1)
• The prototype has the text fading in and moving 200px over 250 milliseconds.
• These exact values are not critical. Consider it a starting point. This is just what was used in the prototype.

We should not use this animation if you have reduce motion turned on. We should also not use this when the dropdown is narrow enough to wrap to 2 lines.

https://hg.mozilla.org/mozilla-central/rev/453666160d92

Closing this as verified fixed as the verification was included in the pre-release test run.