Not sure whether this ought to be done or not. Certainly abstracts [that's the traditional word for "TL;DR" and it also has the advantage of not being pejorativ

Not sure whether this ought to be done or not. Certainly abstracts [that's the traditional word for "TL;DR" and it also has the advantage of not being pejorative] would be a useful addition to the web, but I don't know whether a browser plug-in would be the best way to do it. Off the top of my head, encouraging authors to provide their own is a Good Thing, but they can easily incorporate that into their own websites, so no plug-in is needed. What is really needed is a culture that encourages such things (as, for example, the culture surrounding academic writing has, for decades). As for off-site abstracts, might including such things in sites like HN (see the comment by sorbus) be an effective way of presenting them? And sites like HN already include the voting.