User sash

This idea is only about appearance. Currently scrolling works well though I'd make it in other way. It seems that header has position: fixed/absolute/relative set. And scrollbar is on the right from header which looks weird. Instead I'd not...

Make popup stay there while mouse is over the big picture, so I could save it without opening image in another tab Proposed by shionsan

All rules are cleared when pressing cancel button in "Restore from backup" dialog on preferences page