When changing a frame's size using logical coordinates, it makes more sense for the frame's logical position to stay unchanged, rather than its physical origin. Fixing this doesn't currently affect any reftests (https://treeherder.mozilla.org/#/jobs?repo=try&revision=c011056def55), but will be helpful during the conversion of table layout (which is what brought it to my attention).

Comment on attachment 8622047 [details] [diff] [review] Logical-coordinate versions of nsIFrame::SetSize should maintain the frame's logical position Review of attachment 8622047 [details] [diff] [review]: ----------------------------------------------------------------- Yes, this looks good, and as far as I can tell there aren't any callers of SetSize that already do this (a concern I brought up on IRC)