If easy to make, something I think that would be useful would be something like this:
This would be showing an icon with a little marker next to it if there is anything ‘saved on the page’ on the icon for the program in the toolbar of your browser. Such as a highlight. This popup can be a great indicator when you are flicking through a ton of websites that something is relevant to you.
Not sure how useful it would be a ton of people, but for me at least I could see it having a use.
I was just scrolling to the end of a long page and highlighting something at the bottom of it and realised how useless that highlight would be for me unless scrolling to look for it specifically. I would likely entirely forget there was a highlight at all and try to skim read the whole website trying to find the information before sighting the highlight at the end that was created to stop me skimming in the first place. As I don’t place highlights on every page my native disposition to skim would over-weigh looking for a highlight, unless there was a popup to alert me closer to the top such as on the icon itself.