User Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:44.0) Gecko/20100101 Firefox/44.0 Build ID: 20160210153822 Steps to reproduce: Animate the position of a position:relative parent element, which contains a fixed position element within it, using either JavaScript or CSS3 transitions. https://jsfiddle.net/b700ja5a/1/ Actual results: The fixed element animated in a stuttering manner, and/or became disconnected (not correctly relative) from it's parent element. Expected results: The fixed element should animate as smoothly as the parent element, and should stay at the correct position through out all points in the animation.

Regression window: https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=f5a441d6929f&tochange=df6702c41ddd Regressed by: Bug 157681

The regression bug is assigned to ehsan and reviewed by dbaron so I'm not sure what the need-info request is expecting of me here. Can you clarify?

I was thinking that the regressing bug was a different bug that I thought you had worked on involving avoiding reflow. My mistake.

Took a while for this to get discovered, but it's been found twice recently.