When I was first making the switch, MaterialFox was a godsend. It essentially made Firefox look identical (even better in some regards) to Chrome, including the tab treatment that your friend prefers. Unfortunately it doesn’t look like it’s being actively maintained anymore - you can have your friend give this fork a try, but even that one looks like it was last updated 8 months ago.
When I was first making the switch, MaterialFox was a godsend. It essentially made Firefox look identical (even better in some regards) to Chrome, including the tab treatment that your friend prefers. Unfortunately it doesn’t look like it’s being actively maintained anymore - you can have your friend give this fork a try, but even that one looks like it was last updated 8 months ago.