A number of issues here:
The items in the popup aren't on the right side, they also don't draw in RTL mode (words are not in RTL order)
The selected element doesn't draw on the right side and also doesn't draw with the selected item's text direction.
Created attachment 214207 [details]
Comment on attachment 214207 [details]
r=me. Great to get rid of another platform-specific test result!