Technically, they're not manipulating the clipboard at all. That is definitely disallowed by browsers. What they are doing is extending the selection to an invi

Technically, they're not manipulating the clipboard at all. That is definitely disallowed by browsers. What they are doing is extending the selection to an invisible part of the page, so you're copying more than you bargained for. But without being able to manipulate selections, some nice features of certain sites would be lost. (e.g. the "share" link in StackOverflow automatically selects the URL for you so you only need to press Ctrl-C, instead of having to select it manually.)