Created attachment 316865 [details]
Use "Find in page" in that text case to search "text" and highlight the single search match. Then scroll the overflow node: The highlighted text does not moved with the content of the overflow node.
Extracting this from bug 163911, as that seems orthogonal.
Created attachment 335689 [details]
This is an extended testcase, showing that dynamic scrolls of the main frame or of the subframe make the selection disappear (contrary to desktop).
So to summarize:
- User scroll of a the main frame with hightlighted text works.
- User scroll of a subframe with hightlighted text does not update the position of the highlighted text.
- Programmatic scroll of the main frame or a subframe with hightlighted text makes the selection disappear.