[marginalia_nu]

They're basically the same. Browsers started blocking popups because they were almost always misused. Pop-overs took their place because they're somewhat less trivially blockable.

[The_Colonel]

The big difference is that there are very few valid use cases for popups, but many useful ones for popovers.

[marginalia_nu]

Keep in mind this was a time when virtually all state was kept serverside. Basically anything you could do with a popover you could do with a popup, and there were definitely benign uses of them.